The Platform for Privacy Preferences 1.0 (P3P1.0) Specification

W3C Working Draft 28 September 2001

This Version:: http://www.w3.org/TR/2001/WD-P3P-20010928
Latest Public Version:: http://www.w3.org/TR/P3P/
Previous Version:: http://www.w3.org/TR/2001/WD-P3P-20010924
Editor:: Massimo Marchiori, W3C/MIT/UNIVE, (massimo@w3.org)
Authors:: Lorrie Cranor, AT&T; Marc Langheinrich, ETH Zurich; Massimo Marchiori, W3C/MIT/UNIVE; Martin Presler-Marshall, IBM; Joseph Reagle, W3C/MIT

Abstract

This is the specification of the Platform for Privacy Preferences (P3P). This document, along with its normative references, includes all the specification necessary for the implementation of interoperable P3P applications.

Status of This Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. The latest status of this document series is maintained at the W3C.

This is the 28 September 2001 Last Call Working Draft of the Platform for Privacy Preferences 1.0 (P3P1.0) Specification, for review by W3C members and other interested parties. This Draft has been produced by the P3P Specification Working Group [member only] as part of the P3P Activity. The 24 September Last Call Draft was republished to include a missing change already approved by the Working Group (an embedded DATASCHEMA is now child of POLICIES rather than of POLICY).

The current draft is a revision of the 15 December 2000 Candidate Recommendation Draft. Due to substantive changes based on feedback from implementers, the Working Group has agreed [members only] to return this draft to Last Call to invite comments and input from W3C Members and the community at large. A change log with a summary of the modifications occurred from the 15 December 2000 Candidate Recommendation is included at the end of this document for convenience. Because these changes are based on solid implementation experience, the P3P Specification Group maintains all the Candidate Recommendation milestones and expects to request Proposed Recommendation after all those milestones and comments from this Last Call are properly addressed.

The last call review period ends 15 October 2001. Please send review comments before the review period ends to www-p3p-public-comments@w3.org (publicly archived).

The milestones are:

at least one P3P user agent implementation integrated into an HTTP user agent capable of fetching HTML files that includes all of the functionality required and recommended by this specification
a second P3P user agent implementation of each specified function (these functions may be demonstrated across several partial P3P implementations or they may be demonstrated in a second full P3P implementation)
at least one special-purpose tool for generating P3P policies and policy reference files
at least one tool for converting full P3P policies to compact policies
at least 10 P3P-enabled production web sites
at least one web site that illustrates each of the example scenarios in Section 2.5 of the P3P1.0 specification as well as at least one web site that uses mini-policies (these may be either production web sites or demonstration sites)

Furthermore, before requesting that this specification be advanced to Proposed Recommendation status, the Working Group will:

Prepare a W3C Note describing RDF data models representing P3P policies and policy reference files.
Submit an Internet Draft to the IETF describing the P3P header and request that an RFC be issued documenting this header.
Prepare a set of test policies and policy reference files that user agent implementers can use to demonstrate that their implementations behave correctly. This should include examples of policies that contain syntax errors.
Specify the appropriate behavior for user agents upon encountering a policy with invalid syntax.

The working group also encourages implementers to explore the possibility of implementations in web proxies and mobile devices, as well as implementations that can import user preferences using the [APPEL] language.

A list of current public W3C Working Drafts can be found at http://www.w3.org/TR.

Introduction
Referencing Policies
Policy Syntax and Semantics
Compact Policies
Data schemas
Appendices
Appendix 1: References (Normative)
Appendix 2: References (Non-normative)
Appendix 3: The P3P base data schema Definition (Normative)
Appendix 4: XML Schema Definition (Normative)
Appendix 5: XML DTD Definition (Non-normative)
Appendix 6: ABNF Notation (Non-normative)
Appendix 7: P3P Guiding Principles (Non-normative)
Appendix 8: Working Group Contributors (Non-normative)

1. Introduction

The Platform for Privacy Preferences Project (P3P) enables Web sites to express their privacy practices in a standard format that can be retrieved automatically and interpreted easily by user agents. P3P user agents will allow users to be informed of site practices (in both machine- and human-readable formats) and to automate decision-making based on these practices when appropriate. Thus users need not read the privacy policies at every site they visit.

Although P3P provides a technical mechanism for ensuring that users can be informed about privacy policies before they release personal information, it does not provide a technical mechanism for making sure sites act according to their policies. Products implementing this specification MAY provide some assistance in that regard, but that is up to specific implementations and outside the scope of this specification. However, P3P is complementary to laws and self-regulatory programs that can provide enforcement mechanisms. In addition, P3P does not include mechanisms for transferring data or for securing personal data in transit or storage. P3P may be built into tools designed to facilitate data transfer. These tools should include appropriate security safeguards.

1.1 The P3P1.0 Specification

The P3P1.0 specification defines the syntax and semantics of P3P privacy policies, and the mechanisms for associating policies with Web resources. P3P policies consist of statements made using the P3P vocabulary for expressing privacy practices. P3P policies also reference elements of the P3P base data schema -- a standard set of data elements that all P3P user agents should be aware of. The P3P specification includes a mechanism for defining new data elements and data sets, and a simple mechanism that allows for extensions to the P3P vocabulary.

1.1.1 Goals and Capabilities of P3P1.0

P3P version 1.0 is a protocol designed to inform Web users of the data-collection practices of Web sites. It provides a way for a Web site to encode its data-collection and data-use practices in a machine-readable XML format known as a P3P policy. The P3P specification defines:

A standard schema for data a Web site may wish to collect, known as the "P3P base data schema"
A standard set of uses, recipients, data categories, and other privacy disclosures
An XML format for expressing a privacy policy
A means of associating privacy policies with Web pages or sites, and cookies
A mechanism for transporting P3P policies over HTTP

The goal of P3P version 1.0 is twofold. First, it allows Web sites to present their data-collection practices in a standardized, machine-readable, easy-to-locate manner. Second, it enables Web users to understand what data will be collected by sites they visit, how that data will be used, and what data/uses they may "opt-out" of or "opt-in" to.

1.1.2 Example of P3P in Use

As an introduction to P3P, let us consider one common scenario that makes use of P3P. Claudia has decided to check out a store called CatalogExample, located at http://www.catalog.example.com/. Let us assume that CatalogExample has placed P3P policies on all their pages, and that Claudia is using a Web browser with P3P built in.

Claudia types the address for CatalogExample into her Web browser. Her browser is able to automatically fetch the P3P policy for that page. The policy states that the only data the site collects on its home page is the data found in standard HTTP access logs. Now Claudia's Web browser checks this policy against the preferences Claudia has given it. Is this policy acceptable to her, or should she be notified? Let's assume that Claudia has told her browser that this is acceptable. In this case, the homepage is displayed normally, with no pop-up messages appearing. Perhaps her browser displays a small icon somewhere along the edge of its window to tell her that a privacy policy was given by the site, and that it matched her preferences.

Next, Claudia clicks on a link to the site's online catalog. The catalog section of the site has some more complex software behind it. This software uses cookies to implement a "shopping cart" feature. Since more information is being gathered in this section of the Web site, the Web server provides a separate P3P policy to cover this section of the site. Again, let's assume that this policy matches Claudia's preferences, so she gets no pop-up messages. Claudia continues and selects a few items she wishes to purchase. Then she proceeds to the checkout page.

The checkout page of CatalogExample requires some additional information: Claudia's name, address, credit card number, and telephone number. Another P3P policy is available that describes the data that is collected here and states that her data will be used only for completing the current transaction, her order.

Claudia's browser examines this P3P policy. Imagine that Claudia has told her browser that she wants to be warned whenever a site asks for her telephone number. In this case, the browser will pop up a message saying that this Web site is asking for her telephone number, and explaining the contents of the P3P statement. Claudia can then decide if this is acceptable to her. If it is acceptable, she can continue with her order; otherwise she can cancel the transaction.

Alternatively, Claudia could have told her browser that she wanted to be warned only if a site is asking for her telephone number and was going to give it to third parties and/or use it for uses other than completing the current transaction. In that case, she would have received no prompts from her browser at all, and she could proceed with completing her order.

Note that this scenario describes one hypothetical implementation of P3P. Other types of user interfaces are also possible.

1.1.3 P3P Policies

P3P policies use an XML encoding of the P3P vocabulary to to provide contact information for the legal entity making the representation of privacy practices in a policy, enumerate the types of data or data elements collected, and explain how the data will be used. In addition, policies identify the data recipients, and make a variety of other disclosures including information about dispute resolution, and the address of a site's human-readable privacy policy. P3P policies must cover all relevant data elements and practices (but note that legal issues regarding law enforcement demands for information are not addressed by this specification; it is possible that a site that otherwise abides by its policy of not redistributing data to others may be required to do so by force of law). P3P declarations are positive, meaning that sites state what they do, rather than what they do not do. The P3P vocabulary is designed to be descriptive of a site's practices rather than simply an indicator of compliance with a particular law or code of conduct. However, user agents may be developed that can test whether a site's practices are compliant with a law or code.

P3P policies represent the practices of the site. Intermediaries such as telecommunication providers, Internet service providers, proxies and others may be privy to the exchange of data between a site and a user, but their practices may not be governed by the site's policies.

1.1.4 P3P User Agents

P3P1.0 user agents can be built into Web browsers, browser plug-ins, or proxy servers. They can also be implemented as Java applets or JavaScript; or built into electronic wallets, automatic form-fillers, or other user data management tools. P3P user agents look for references to a P3P policy at a well-known location, in P3P headers in HTTP responses, and in P3P link tags embedded in HTML content. These references indicate the location of a relevant P3P policy. User agents can fetch the policy from the indicated location, parse it, and display symbols, play sounds, or generate user prompts that reflect a site's P3P privacy practices. They can also compare P3P policies with privacy preferences set by the user and take appropriate actions. P3P can perform a sort of "gate keeper" function for data transfer mechanisms such as electronic wallets and automatic form fillers. A P3P user agent integrated into one of these mechanisms would retrieve P3P policies, compare them with user's preferences, and authorize the release of data only if a) the policy is consistent with the user's preferences and b) the requested data transfer is consistent with the policy. If one of these conditions is not met, the user might be informed of the discrepancy and given an opportunity to authorize the data release themselves.

1.1.5 Implementing P3P1.0 on Servers

Web sites can implement P3P1.0 on their servers by translating their human-readable privacy policies into P3P syntax and then publishing the resulting files along with a policy reference file that indicates the parts of the site to which the policy applies. Automated tools can assist site operators in performing this translation. P3P1.0 can be implemented on existing HTTP/1.1-compliant Web servers without requiring additional or upgraded software. Servers may publish their policy reference files at a well-known location, or they may reference their P3P policy reference files in HTML content using a link tag. Alternatively, compatible servers may be configured to insert a P3P extension header into all HTTP responses that indicates the location of a site's P3P policy reference file.

Web sites have some flexibility in how they use P3P: they can opt for one P3P policy for their entire site or they can designate different policies for different parts of their sites. A P3P policy MUST cover all data generated or exchanged as part of a site's HTTP interactions with visitors. In addition, some sites may wish to write policies that cover all data an entity collects, regardless of how the data is collected.

1.1.6 Future Versions of P3P

Significant sections were removed from earlier drafts of the P3P1.0 specification in order to facilitate rapid implementation and deployment of a P3P first step. A future version of the P3P specification might incorporate those features after P3P1.0 is deployed. Such specification would likely include improvements based on feedback from implementation and deployment experience as well as four major components that were part of the original P3P vision but not included in P3P1.0:

a mechanism to allow sites to offer a choice of P3P policies to visitors
a mechanism to allow visitors (through their user agents) to explicitly agree to a P3P policy
mechanisms to allow for non-repudiation of agreements between visitors and Web sites
a mechanism to allow user agents to transfer user data to services

1.2 About this Specification

This document, along with its normative references, includes all the specification necessary for the implementation of interoperable P3P applications.

The [ABNF] notation used in this specification is specified in RFC2234 and summarized in Appendix 6. However, note that in the case of XML syntax, such ABNF syntax is only a grammar representative of the XML syntax (for example, all the syntactic flexibilities of XML are also implicitly included; e.g. whitespace rules, quoting using either single quote (') or double quote ("), character escaping, comments, case sensitivity, order of attributes). All the XML syntax defined in this specification MUST conform to the XML Schema for P3P (see Appendix 4), which is the normative definition. For non-XML syntax (like, for example, in HTTP headers), the ABNF notation is the normative one.

In the sections that follow a number of XML elements are introduced. Each element is given in angle brackets ("<element>"), followed by a list of valid attributes. All listed attributes are optional, except when tagged as mandatory. Note that many XML elements are shown in the BNF with separate beginning and ending tags to allow optional elements inside them. If no elements are included, then, following standard XML rules, a self-closing element may be used instead.

The following key words are used throughout the document and have to be read as interoperability requirements. This specification uses words as defined in RFC2119 [KEY] for defining the significance of each particular requirement. These words are:

MUST or MUST NOT: This word or the adjective "required" means that the item is an absolute requirement of the specification.
SHOULD or SHOULD NOT: This word or the adjective "recommended" means that there may exist valid reasons in particular circumstances to ignore this item, but the full implications should be understood and the case carefully weighed before choosing a different course.
MAY: This word or the adjective "optional" means that this item is truly optional. One vendor may choose to include the item because a particular marketplace requires it or because it enhances the product, for example; another vendor may omit the same item.

1.3 Terminology

Character: Strings consist of a sequence of zero or more characters, where a character is defined as in the XML Recommendation [XML]. A single character in P3P thus corresponds to a single Unicode abstract character with a single corresponding Unicode scalar value (see [UNICODE]).
Data Element: An individual data entity, such as last name or telephone number. For interoperability, P3P1.0 specifies a base set of data elements.
Data Category: A significant attribute of a data element or data set that may be used by a trust engine to determine what type of element is under discussion, such as physical contact information. P3P1.0 specifies a set of data categories.
Data Set: A known grouping of data elements, such as "user.home-info.postal". The P3P1.0 base data schema specifies a number of data sets.
Data Schema: A collection of data elements and sets defined using the P3P1.0 DATASCHEMA element. P3P1.0 defines a standard data schema called the P3P base data schema.
Data Structure: A hierarchical description of a set of data elements. A data set can be described according to its data structure. P3P1.0 defines a set of basic datastructures that are used to describe the data sets in the P3P base data schema.
Equable Practice: A practice that is very similar to another in that the purpose and recipients are the same or more constrained than the original, and the other disclosures are not substantially different. For example, two sites with otherwise similar practices that follow different -- but similar -- sets of industry guidelines.
Identified Data: Data that reasonably can be used by the data collector to identify an individual.
Policy: A collection of one or more privacy statements together with information asserting the identity, URI, assurances, and dispute resolution procedures of the service covered by the policy.
Practice: The set of disclosures regarding data usage, including purpose, recipients, and other disclosures.
Preference: A rule, or set of rules, that determines what action(s) a user agent will take. A preference might be expressed as a formally defined computable statement (e.g., the [APPEL] preference exchange language).
Purpose: The reason(s) for data collection and use.
Repository: A mechanism for storing user information under the control of the user agent.
Safe Zone: Part of a Web site where the service provider performs only minimal data collection, and any data that is collected is used only in ways that would not reasonably identify an individual.
Service: A program that issues policies and (possibly) data requests. By this definition, a service may be a server (site), a local application, a piece of locally active code, such as an ActiveX control or Java applet, or even another user agent.
Service Provider (Data Controller, Legal Entity): The person or legal entity which offers information, products or services from a Web site, collects information, and is responsible for the representations made in a practice statement.
Statement: A P3P statement is a set of privacy practice disclosures relevant to a collection of data elements.
URI: A Uniform Resource Identifier used to locate Web resources. For definitive information on URI syntax and semantics, see [URI]. URIs that appear within XML or HTML have to be treated as specified in [CHARMODEL], section Character Encoding in URI References. This does not apply to URIs appearing in HTTP header fields; the URIs there should always be fully escaped.
User: An individual (or group of individuals acting as a single entity) on whose behalf a service is accessed and for which personal data exists.
User Agent: A program whose purpose is to mediate interactions with services on behalf of the user under the user's preferences. A user may have more than one user agent, and agents need not reside on the user's desktop, but any agent must be controlled by and act on behalf of only the user. The trust relationship between a user and his or her agent may be governed by constraints outside of P3P. For instance, an agent may be trusted as a part of the user's operating system or Web client, or as a part of the terms and conditions of an ISP or privacy proxy.

2. Referencing Policies

2.1 Overview and Purpose of Policy References

Locating a P3P policy is one of the first steps in the operation of the P3P protocol. Services use policy references to state what policy applies to a specific URI or set of URIs. User agents use policy references to locate the privacy policy that applies to a page, so that they can process that policy for the benefit of their user.

Policy references are used extensively as a performance optimization. P3P policies are typically several kilobytes of data, while a URI that references a privacy policy is typically less than 100 bytes. In addition to the bandwidth savings, policy references also reduce the need for computation: policies can be uniquely associated with URIs, so that a user agent need only parse and process a policy once rather than process it with every document to which the policy applies. Furthermore, by placing the information about relevant policies in a centralized location, Web site administration is simplified.

A policy reference file is used to associate P3P policies with certain regions of URI-space. The policy reference file is an XML (see [XML]) file that can specify the policy for a single Web document, portions of a Web site, or for an entire site. The policy reference file may refer to one or more P3P policies; this allows for a single reference file to cover an entire site, even if different P3P policies apply to different portions of the site.The policy reference file is used to make any or all of the following statements:

The URI where a P3P policy is found
The URIs or regions of URI-space covered by this policy
The URIs or regions of URI-space not covered by this policy
The regions of URI-space for embedded content on other servers that are covered by this policy
The cookies that are or are not covered by this policy
The access methods for which this policy is applicable
The period of time for which these claims are considered to be valid

All of these statements are made in the body of the policy reference file.

2.2 Locating Policy Reference Files

This section describes the mechanisms used to indicate the location of a policy reference file. Detailed syntax is also given for the supported mechanisms.

The location of the policy reference file can be indicated using one of three mechanisms. The policy reference file may be located in a predefined "well-known" location, or a document may indicate a policy reference file through an HTML link tag, or through an HTTP header.

Note that if user agents support retrieving HTML content over HTTP, they MUST handle all three mechanisms listed above interchangeably. See also the requirements for non-ambiguity.

Note that policies are applied at the level of HTTP entities. An entity, retrieved by fetching a URI, has a P3P policy associated with it. A "page" from the user's perspective may be composed of multiple HTTP entities; each entity may have its own P3P policy associated with it. As a practical note, however, placing many different P3P policies on different entities on a single page may make rendering the page and informing the user of the relevant policies difficult for user agents. Additionally, services are recommended to attempt to craft their policy reference files such that a single policy reference file covers any given "page"; this will speed up the user's browsing experience.

For a user agent to process the policy that applies to a given entity, it must locate the policy reference file for that entity, fetch the policy reference file, parse the policy reference file, fetch any required P3P policies, and then parse the P3P policy or policies.

This document does not specify how P3P policies may be associated with documents retrieved by means other than HTTP. However, it does not preclude future development of mechanisms for associating P3P policies with documents retrieved over other protocols. Furthermore, additional methods of associating P3P policies with documents retrieved using HTTP may be developed in the future.

2.2.1 Well-Known Location

Web sites using P3P SHOULD place a policy reference file in a "well-known" location. To do this, a policy reference file would be placed in the site's /w3c directory, under the name p3p.xml. Thus a user agent could request this policy reference file by using a GET request for the resource /w3c/p3p.xml.

Note that sites are not required to use this mechanism; however, by using this mechanism, sites can ensure that their P3P policy will be accessible to user agents before any other resources are requested from the site. This will reduce the need for user agents to access the site using safe zone practices. Additionally, if a site chooses to use this mechanism, the policy reference file located in the well-known location is not required to cover the entire site. For example, sites where not all of the content is under the control of a single organization MAY choose not to use this mechanism, or MAY choose to post a policy reference file which covers only a limited portion of the site.

Use of the well-known location for a policy reference file does not preclude use of other mechanisms for specifying a policy reference file. Portions of the site MAY use any of the other supported mechanisms to specify a policy reference file, so long as the non-ambiguity requirements are met.

For example, imagine a shopping-mall Web site run by the MallExample company. On their Web site (mall.example.com), companies offering goods or services at the mall would get a company-specific subtree of the site, perhaps in the path /companies/company-name. The MallExample company may choose to put a policy reference file in the well-known location which covers all of their site except the /companies subtree. Then if the ShoeStoreExample company has some content in /companies/shoestoreexample, they could use one of the other mechanisms to indicate the location of a policy reference file covering their portion of the mall.example.com site.

One case where using the well-known location for policy reference files is expected to be particularly useful is in the case of a site which has divided its content across several hosts. For example, consider a site which uses a different logical host for all of its Web-based applications than for its static HTML content. The other mechanisms allowed for specifying the location of a policy reference file require that some URI on the host being accessed must be fetched to locate the policy reference file. However, the well-known location mechanism has no such requirement. Consider the example of an HTML form located on www.example.com. Imagine that the action URI on that form points to server cgi.example.com. The policy reference file that covers the form is unable to make any statements about the action URI that processes the form. However, the site administrator publishes a policy reference file at http://cgi.example.com/w3c/p3p.xml that covers the action URI, thus enabling a user agent to easily locate the P3P policy that applies to the action URI before submitting the form contents.

2.2.2 HTTP Headers

Any document retrieved by HTTP MAY point to a policy reference file through the use of a new response header, the P3P header ([P3P-HEADER]). If a site is using P3P headers, it SHOULD include this on responses for all appropriate request methods, including HEAD and OPTIONS requests.

The P3P header gives one or more comma-separated directives. The syntax follows:

[1]	p3p-header	=	`P3P: ` p3p-header-field *(`,` p3p-header-field)
[2]	p3p-header-field	=	policy-ref-field \| compact-policy-field \| extension-field
[3]	policy-ref-field	=	`policyref="` URI `"`
[4]	extension-field	=	token [`=` (token \| quoted-string) ]
Here, `URI` is defined as per RFC 2396 [URI], `token` and `quoted-string` are defined by [HTTP1.1].

In keeping with the rules for other HTTP headers, the name of the P3P header may be written with any casing. The contents should be specified using the casing precisely as specified in this document.

The policyref directive gives a URI which specifies the location of a policy reference file which may reference the P3P policy covering the document that pointed to the reference file, and possibly others as well. When the policyref attribute is a relative URI, that URI is interpreted relative to the request URI. Note that fetching the URI given in the policyref directive MAY result in a 300-class HTTP return code (redirection); user agents MUST interpret those redirects with normal HTTP semantics. Services should note, of course, that use of redirects will increase the time required for user agents to find and interpret their policies. The policyref URI MUST NOT be used for any other purpose beyond locating and referencing P3P policies.

The compact-policy-field is used to specify "compact policies". This is described in Section 4.

User agents which find unrecognized directives (in the extension-fields) MUST ignore the unrecognized directives. This is to allow easier deployment of future versions of P3P.

Example 2.1:

1. Client makes a GET request.

GET /index.html HTTP/1.1
Host: catalog.example.com
Accept: */*
Accept-Language: de, en
User-Agent: WonderBrowser/5.2 (RT-11)

2. Server returns content and the P3P header pointing to the policy of the page.

HTTP/1.1 200 OK
P3P: policyref="http://catalog.example.com/P3P/PolicyReferences.xml"
Content-Type: text/html
Content-Length: 7413
Server: CC-Galaxy/1.3.18

2.2.3 The HTML `link` Tag

Servers MAY serve HTML content with embedded link tags that indicate the location of the relevant P3P policy reference file. This use of P3P does not require any change in the server behavior.

The link tag encodes the policy reference information that could be expressed using the P3P header. The link tag takes the following form:

[5]	p3p-link-tag	=	`<link rel="P3Pv1" href="` URI `">`
Here, `URI` is defined as per RFC 2396 [URI].

When the href attribute is a relative URI, that URI is interpreted relative to the request URI.

In order to illustrate with an example the use of the link tag, we consider the policy reference expressed in Example 2.1 using HTTP headers. That example can be equivalently expressed using the link tag with the following piece of HTML:

<link rel="P3Pv1"
    href="http://catalog.example.com/P3P/PolicyReferences.xml">

Finally, note that since the p3p-link-tag is embedded in an HTML document, its character encoding will be the same as that of the HTML document. In contrast to P3P policy and policy reference documents (see section 2.3 and section 3 below), the p3p-link-tag need not be encoded using [UTF-8]. Note also that the link tag is not case sensitive

2.2.4 HTTP ports and other protocols

The mechanisms described here MAY be used for HTTP transactions over any underlying protocol. This includes plain-text HTTP over TCP/IP connections as well as encrypted HTTP over SSL connections, as well as HTTP over any other communications protocol network designers wish to implement.

URLs MAY contain TCP/IP port numbers, as specified in RFC 2396 [URI]. For the purposes of P3P, the different ports on a single host MUST be considered to be separate "sites". Thus, for example, the policy reference file at the well-known location for www.example.com on port 80 (http://www.example.com/w3c/p3p.xml) would not give any information about the policies which apply to www.example.com when accessed over SSL (as the SSL communication would take place on a different port, 443 by default).

2.3 Policy Reference File Syntax and Semantics

This section explains the contents of policy reference files in detail.

2.3.1 Example Policy Reference File

Consider the case of a Web site wishing to make the following statements:

P3P policy /P3P/Policies.xml#first applies to the entire site, except the subtrees /catalog, /cgi-bin, and /servlet.
P3P policy /P3P/Policies.xml#second applies to all documents in the /catalog directory (and its subdirectories).
P3P policy /P3P/Policies.xml#third applies to all documents in the /cgi-bin and /servlet directories (and their subdirectories), except for /servlet/unknown.
No statement is made about what P3P policy applies to /servlet/unknown.
These statements are valid for 2 days.

These statements could be represented by the following piece of XML:

Example 2.2:

<META xmlns="http://www.w3.org/2001/09/P3Pv1">
 <POLICY-REFERENCES>
  <EXPIRY max-age="172800"/>

    <POLICY-REF about="/P3P/Policies.xml#first">
      <INCLUDE>/*</INCLUDE>
      <EXCLUDE>/catalog/*</EXCLUDE>
      <EXCLUDE>/cgi-bin/*</EXCLUDE>
      <EXCLUDE>/servlet/*</EXCLUDE>
    </POLICY-REF>

    <POLICY-REF about="/P3P/Policies.xml#second">
      <INCLUDE>/catalog/*</INCLUDE>
    </POLICY-REF>

    <POLICY-REF about="/P3P/Policies.xml#third">
      <INCLUDE>/cgi-bin/*</INCLUDE>
      <INCLUDE>/servlet/*</INCLUDE>
      <EXCLUDE>/servlet/unknown</EXCLUDE>
    </POLICY-REF>

 </POLICY-REFERENCES>
</META>

Note this example also includes via EXPIRY a relative expiry time in the document (cf. Section 2.3.2.3.2).

2.3.2 Policy Reference File Definition

This section defines the syntax and semantics of P3P policy reference files. All policies MUST be encoded using [UTF-8]. P3P servers MUST encode their policy references using this syntax. P3P user agents MUST be able to parse this syntax.

One significant point to make about the syntax of policy reference files is that the syntax defined here does not have an extension mechanism. The syntax for P3P policies has a powerful extension mechanism, but that mechanism is not supported for policy reference files.

2.3.2.1 Policy reference file processing

2.3.2.1.1 Significance of order

A policy reference file may contain multiple POLICY-REF elements. If it does contain more than one element, they MUST be processed by user agents in the order given in the file. When a user agent is attempting to determine what policy applies to a given URI, it MUST use the first POLICY-REF element in the policy reference file which applies to that URI.

Note that each POLICY-REF may contain multiple INCLUDE, EXCLUDE, METHOD, COOKIE-INCLUDE, and COOKIE-EXCLUDE elements and that all of these elements within a given POLICY-REF MUST be considered together to determine whether the POLICY-REF applies to a given URI. Thus, it is not sufficient to find an INCLUDE element that matches a given URI, as EXCLUDE or METHOD elements may serve as modifiers that cause the POLICY-REF not to match.

2.3.2.1.2 Wildcards in policy reference files

Policy reference files make statements about what policy applies to a given URI. Policy reference files support a simple wildcard character to allow making statements about regions of URI-space. The character asterisk ("*") is used to represent a sequence of 0 or more of any character. No other special characters (such are those found in regular expressions) are supported. Note that since the asterisk is also a legal character in URIs ([URI]), some special conventions have to be followed when encoding such "extended URIs" in a policy reference file:

URIs represented in policy-ref files MUST be properly escaped, as in [URI].
P3P user agents MUST escape any characters which should be escaped, as according to [URI], before attempting to match a URI for a policy.
P3P user agents MUST un-escape any escaped sequences which resolve to URI-legal characters, according to [URI], before attempting to match a URI for a policy, EXCEPT
Literal '*'s in URIs MUST be escaped by P3P user agents before attempting to match a URI for a policy.
P3P user agents MUST ignore any URI pattern that does not conform to [URI]

The wildcard character MAY be used in the INCLUDE and EXCLUDE elements, in the COOKIE-INCLUDE and COOKIE-EXCLUDE elements, and in the HINT element.

2.3.2.2 The `META` and `POLICY-REFERENCES` elements

The META element contains a complete policy reference file. Optionally, one POLICIES element can follow. Additionally, other XML markup MAY follow the POLICY-REFERENCES (or POLICIES, if present) element, although that markup MUST be ignored by any P3P1.0 user agent.

<POLICY-REFERENCES>: This element MAY contain one or more POLICY-REF (policy reference) elements. It MAY also contain one EXPIRY element (indicating their expiration time), and one or more HINT element.

[6]	prf	=	`<META xmlns="http://www.w3.org/2001/09/P3Pv1">` policyrefs [policies] PCDATA "</META>"
[7]	policyrefs	=	"<POLICY-REFERENCES>" [expiry] policyref hint "</POLICY-REFERENCES>"
Here `PCDATA` is defined in [XML].

2.3.2.3 Policy reference file lifetimes and the `EXPIRY` element

2.3.2.3.1 Motivation and mechanism

It is desirable for servers to inform user agents about how long they can use the claims made in a policy reference file. By enabling clients to cache the contents of a policy reference file, it reduces the time required to process the privacy policy associated with a Web page. This also reduces load on the network. In addition, clients that don't have a valid policy reference file for a URI will need to use "safe zone" practices for their requests. If clients have policy reference files that they know are still valid, then they can make more informed decisions on how to proceed.

In order to achieve these benefits, policy reference files SHOULD contain an EXPIRY element, which indicates the lifetime of the policy reference file. If the policy reference file does not contain an EXPIRY element, then it is given a 24-hour lifetime.

The lifetime of a policy reference file tells user agents how long they can rely on the claims made in the policy reference file. By setting the lifetime of a policy reference file, the publishing site agrees that the policies mentioned in the policy reference file are appropriate for the lifetime of the policy reference file. For example, if a policy reference file has a lifetime of 3 days, then a user agent need not reload that file for 3 days, and can assume that the references made in that policy reference file are good for 3 days. All of the policy references made in a single policy reference file will receive the same lifetime. The only way to specify different lifetimes for different policy references is to use separate policy reference files.

The same mechanism used to indicate the lifetime of a policy reference file is also used to indicate the lifetime of a P3P policy. Thus P3P POLICIES elements SHOULD have an EXPIRY element associated with them as well. This lifetime applies to all P3P policies contained within that POLICIES element. If there is no EXPIRY element associated with a P3P policy, then it is given a 24-hour lifetime.

When picking a lifetime for policies and policy reference files, sites need to pick a lifetime which balances two competing concerns. One concern is that the lifetime ought to be long enough to allow user agents to receive significant benefits from caching. The other concern is that the site would like to be able to change their policy for new data colleciton without waiting for an extremely long lifetime to expire. It is expected that lifetimes in the range of 1-7 days would be a reasonable balance between these two competing desires. Sites also need to remember the policy update requirements when updating their policies.

When a policy reference file has expired, the information in the policy reference file MUST NOT be used by a user agent until that user agent has successfully revalidated the policy reference file, or has fetched a new copy of the policy reference file.

Note that while user agents are not obligated to revalidate policy reference files or policy files that have not expired, they MAY choose to revalidate those files before their expiry period has passed, in order to reduce the need for using "safe zone" practices. A valid P3P user agent implementation doesn't need to contain a cache for policies and policy reference files, though the implementation will have a better performance if it does.

2.3.2.3.2 The `EXPIRY` element

The EXPIRY element can be used in a policy reference file and/or in a POLICIES element to state how long the policy reference file (or policies) remains valid. The expiry is given as either an absolute expiry time, or a relative expiry time. An absolute expiry time is a time, given in GMT, until which the policy reference file (or policies) is valid. A relative expiry time gives a number of seconds for which the policy reference file (or policies) is valid. This expiry time is relative to the time the policy reference file (or policies) was requested or last revalidated by the client. This computation MUST be done using the time of the original request or revalidation, and the current time, with both times generated from the client's clock. Revalidation is defined in section 13.3 of [HTTP1.1].

The minimum amount of time for any relative expiry time is 24 hours, or 86400 seconds. Any relative expiration time shorter than 86400 seconds MUST be treated as being equal to 86400 seconds in a client implementation. If a client encounters an absolute expiration time that is in the past, it MUST act as if NO policy reference file (or policy) is available. See section 2.4.7 "Absence of Policy Reference File" for the required procedure in such cases.

[8]	expiry	=	"<EXPIRY" (absdate\|reldate) "/>"
[9]	absdate	=	`date="` HTTP-date `"`
[10]	reldate	=	`max-age="` delta-seconds `"`
Here, HTTP-date is defined in section 3.3.1 of [HTTP1.1], and delta-seconds is defined in section 3.3.2 of [HTTP1.1].

2.3.2.3.3 Requesting Policies and Policy Reference Files

In a real-world network, there may be caches which will cache the contents of policies and policy reference files. This is good for increasing the overall network performance, but may have deleterious effects on the operation of P3P if not used correctly. There are two specific concerns:

When a user agent receives a policy reference file (or policy), if it was served from a network cache, the user agent needs to know how long the policy reference file or policy resided in the network cache. This time MUST be subtracted from the lifetime of the policy or policy reference file which uses relative expiry.
When a user agent needs to revalidate a policy reference file (or policy), it needs to make sure that the revalidation fetches a current version of the policy reference file (or policy). For example, consider the case where a user agent holds a policy reference file with a 1 day relative expiry. If the user agent refetches it from a network cache, and the file has been residing in the network cache for 3 days, then the resulting file is useless.

HTTP 1.1 [HTTP1.1] contains powerful cache-control mechanisms to allow clients to place requirements on the operations of network caches; these mechanisms can resolve the problems mentioned above. The specific method will be discussed below.

HTTP 1.0, however, does not provide those more sophisticated cache control mechanisms. An HTTP 1.0 network cache will, in all likelihood, compute a cache lifetime for the policy reference file (or policies) based on the file's last-modified date; the resulting cache lifetime could be significantly longer than the lifetime specified by the EXPIRY element. The network cache could then serve the policy reference file (or policies) to clients beyond the lifetime in the EXPIRY; the result would be that user-agents would receive a useless policy reference file (or policies).

The second problem with HTTP 1.0 network caches is that a user agent has no way to know how long the reference file may have been stored by the network cache. If the policy reference file (or policies) relies on relative expiry, it would then be impossible for the user agent to determine if the reference file's lifetime has already expired, or when it will expire.

Thus, if a user agent is requesting a policy reference file or a policy, and does not know for certain that there are no HTTP 1.0 caches in the path to the origin server, then the request must force an end-to-end revalidation. This can be done with the Pragma: no-cache HTTP request-header. Note that neither HTTP nor P3P define a way to determine if there is a HTTP 1.0-compliant cache in any given network path, so unless the user agent has this information derived from an outside source, it MUST force the end-to-end revalidation.

If the user agent has some way to know that all caches in the network path to the origin server are compliant with HTTP 1.1 (or that there are no caches in the network path to the origin server), then the client MUST do the following:

Use cache-control request-headers to ensure that the received response is not older than its lifetime. This is done with the max-age cache-control setting, with a maximum age significantly less than the lifetime of the policy reference file (or policies). For example, a user agent could send Cache-Control: max-age=43200, thus ensuring that the response is no more than 12 hours old.
Subtract the age of the response from the lifetime of the policy reference file (or policies), if it uses a relative expiry time. The age of the response is given by the Age: HTTP response-header.

Note that it is impossible for a client to accurately predict the amount of latency that may affect an HTTP request. Thus, if the policy reference file covering a request is going to expire soon, clients MAY wish to consider warning their users and/or revalidating the policy reference file before continuing with the request.

2.3.2.3.4 Error handling for policy reference file and policy lifetimes

The following situations have their semantics specifically defined:

An absolute expiry date in the past renders the policy reference file (or policies) useless, as does an invalid or malformed expiry date, whether relative or absolute. In this case, user agents MUST act as if NO policy reference file (or policies) is available. See section 2.4.7 "Absence of Policy Reference File" for the required procedure in such cases.
A relative expiration time shorter than 86400 seconds (1 day) is considered to be equal to 86400 seconds.
When a policy reference file contains more than one EXPIRY element, the first one takes precedence for determining the lifetime of the policy reference file.

2.3.2.4 The `POLICY-REF` element

A policy reference file may refer to multiple P3P policies, specifying information about each. The POLICY-REF element describes attributes of a single P3P policy. Elements within the POLICY-REF element give the location of the policy and specify the areas of URI-space (and cookies) that each policy covers.

POLICY-REF: contains information about a single P3P policy.
about (mandatory attribute): URI reference ([URI]), where the fragment identifier part denotes the name of the policy (given in its name attribute), and the URI part denotes the URI where the policy resides. If this is a relative URI reference, it is interpreted relative to the URI of the policy reference file.

[11]	policy-ref	=	`<POLICY-REF about="` URI-reference `">` include exclude cookie-include cookie-exclude *method-element `</POLICY-REF>`
Here, `URI` is defined as per RFC 2396 [URI].

2.3.2.5 The `INCLUDE` and `EXCLUDE` elements

Each INCLUDE or EXCLUDE element specifies one local URI or set of local URIs. A set of URIs is specified if the wildcard character '*' is used in the URI-pattern. These elements are used to specify the portion of the Web site that is covered by the policy referenced by the enclosing POLICY-REF element.

When INCLUDE (and optionally, EXCLUDE) elements are present in a POLICY-REF element, it means that the policy specified in the about attribute of the POLICY-REF element applies to all the URIs at the requested host corresponding to the local-URI(s) matched by any of the INCLUDEs, but not matched by an EXCLUDE element.

A policy referenced in a policy reference file can be applied only to URIs on the DNS (Domain Name System) host that reference it. The INCLUDE and EXCLUDE elements MUST specify URI patterns relative to the root of the DNS host to which they are applied. This requirement does NOT apply to the location of the P3P policy file (the about attribute on the POLICY-REF element).

If a METHOD element (section 2.3.2.8) specifies one or more methods for an enclosing policy reference, it follows that all methods not mentioned are consequently not covered by this policy. In the case that this is the only policy reference for a given URI prefix, user agents MUST assume that NO policy is in effect for all methods NOT mentioned in the policy reference file. It is legal but pointless to supply a METHOD element without any INCLUDE or COOKIE-INCLUDE elements.

It is legal, but pointless, to supply an EXCLUDE element without any INCLUDE elements; in that case, the EXCLUDE element MUST be ignored by user agents.

Note that the set of URIs specified with INCLUDE and EXCLUDE does not include cookies that might be triggered when requesting one of such URIs: in order to associate policies with cookies, the COOKIE-INCLUDE and COOKIE-EXCLUDE elements are needed.

[12]	include	=	"<INCLUDE>" relativeURI "</INCLUDE>"
[13]	exclude	=	"<EXCLUDE>" relativeURI "</EXCLUDE>"
Here, `relativeURI` is defined as per RFC 2396 [URI], with the addition that the '`*`' character is to be treated as a wildcard, as defined in section 2.3.2.1.2.

2.3.2.6 The `HINT` element

Policy reference hints are a performance optimization that can be used under certain conditions. A DNS host may declare a policy reference for itself using the well-known location, the P3P response header, or the HTML link tag. The host MAY further provide a hint to additional policy references, such as those declared by other hosts. For example, an HTML page might hint at policy references for its hyperlinks, embedded content, and form submission URIs. User agents MAY use the hint mechanism to discover policy references before requesting the affected URIs when the policy references are not available from the well-known location.

Any policy reference file MAY contain zero or more policy reference hints. Each hint is contained in a HINT element, and consists of single host or domain of hosts to which the hinted policy reference can be applied. When using a hint applicable to multiple hosts, the policy reference is expected in the same relative location on each host, but the content may vary according to the host. Therefore, a user agent that finds a policy reference on a particular host via the hint mechanism MUST NOT apply it to another host.

The domain attribute is used to domain-match (possibly using the '*' wildcard) the host(s) to which the hinted policy reference file can be applied. The path attribute specifies the location of the hinted policy reference files relative to the applicable host rather than the policy reference file containing the hint.

Here is an example of HINT elements that hint at the location of policy reference files on the host example.org and on any host in the domain shop.example.com:

Example 2.3:

<HINT domain="example.org" path="/mypolicy/p2.xml"/>
<HINT domain="*.shop.example.com" path="/w3c/prf.xml"/>

If a hinted policy reference file is not found, expired, or otherwise invalid, the user agent MUST ignore the hint. Before using a hinted policy reference, the user agent MUST check the well-known location and give precedence to any policy references directly declared by the host, with the well-known location taking the highest precedence. If a hinted policy reference is not directly declared by the host as expected, the user agent MAY ignore it.

[14]	hint	=	`<HINT domain="` HN `" path="` token `/>`
Here, `HN` and `token` are defined as per RFC 2965 [STATE], with the addition that in `HN` the '`*`' character is to be treated as a wildcard, as defined in section 2.3.2.1.2.

2.3.2.7 The `COOKIE-INCLUDE` and `COOKIE-EXCLUDE` elements

The COOKIE-INCLUDE and COOKIE-EXCLUDE elements are used to associate policies to cookies.

A cookie policy MUST cover any data (within the scope of P3P) that is stored in that cookie or linked via that cookie. It MUST also reference all purposes associated with data stored in that cookie or enabled by that cookie. In addition, any data/purpose stored or linked via a cookie MUST also be put in the cookie policy. In addition, if that linked data is collected by HTTP, then the policy that covers that GET/POST/whatever request must cover that data collection. For example, when CatalogExample asks customers to fill out a form with their name, billing, and shipping information, the P3P policy that covers the form submittal will disclose that CatalogExample collects this data and explain how it is used. If CatalogExample sets a cookie so that it can recognize its customers and observe their behavior on its web site, it would have a separate policy for this cookie. However, if this cookie is also linked to the user's name, billing, and shipping information -- perhaps so CatalogExample can generate custom catalog pages based on where the customer lives -- then that data must also be disclosed in the cookie policy.

For the purpose of this specification, state management mechanisms use either SET-COOKIE or SET-COOKIE2 headers, and cookie-namespace is defined as the value of the NAME, VALUE, Domain and Path attributes, specified in [COOKIES] and [STATE].

Each COOKIE-INCLUDE or COOKIE-EXCLUDE element can be used to match (similarly to INCLUDE and EXCLUDE) the NAME, VALUE, Domain and Path components of a cookie, expressing the cookies which are covered by the policy specified by the about attribute when the cookies are set from the documents on the Web site where the policy reference file resides:

COOKIE-INCLUDE (resp. COOKIE-EXCLUDE): include (resp. exclude) cookies that match the name, value, domain and path attributes
name: match the NAME portion of the cookie
value: match the VALUE portion of the cookie
domain: match the Domain portion of the cookie
path: match the Path portion of the cookie

All four attributes are optional. If an attribute is absent, the COOKIE-INCLUDE (resp. COOKIE-EXCLUDE) will match cookies that have that attribute set to any value.

When COOKIE-INCLUDE (and optionally, COOKIE-EXCLUDE) elements are present in a POLICY-REF element, the policy specified in the about attribute of the POLICY-REF element applies to every cookie that is matched by any COOKIE-INCLUDE's, and not matched by a COOKIE-EXCLUDE element.

A site MUST NOT declare policies for cookies unless the cookies are set by its own site. User agents MUST accordingly interpret COOKIE-INCLUDE and COOKIE-EXCLUDE elements in a policy reference file to determine the policy that applies to cookies. Note that COOKIE-INCLUDE and COOKIE-EXCLUDE are the only mechanisms for associating policies with cookies in policy reference files (see Section 4).

The policy that applies to a cookie applies until the policy expires, even if the associated policy reference file expires prior to policy expiry (but after the cookie was set). If the policy associated with a cookie has expired, then the user agent SHOULD reevaluate the cookie policy before sending the cookie. In addition, user agents MUST use only non-expired policies and policy reference files when evaluating new set-cookie events.

Example 2.4 states that /P3P/Policies.xml#first applies to all cookies.

Example 2.4:

<META xmlns="http://www.w3.org/2001/09/P3Pv1">
 <POLICY-REFERENCES>
    <POLICY-REF about="/P3P/Policies.xml#first">
       <COOKIE-INCLUDE name="*" value="*" domain="*" path="*"/>
    </POLICY-REF>
 </POLICY-REFERENCES>
</META>

Example 2.5 states that /P3P/Policies.xml#first applies to all cookies, except cookies with the cookie name value of "obnoxious-cookie", a domain value of ".example.com", and a path value of "/", and that /P3P/Policies.xml#second applies to all cookies with the cookie name of "obnoxious-cookie", a domain value of ".example.com", and a path value of "/".

Example 2.5:

<META xmlns="http://www.w3.org/2001/09/P3Pv1">
 <POLICY-REFERENCES>
    <POLICY-REF about="/P3P/Policies.xml#first">
       <COOKIE-INCLUDE name="*" value="*" domain="*" path="*"/>
       <COOKIE-EXCLUDE name="obnoxious-cookie" value="*" domain=".example.com" path="/"/>
    </POLICY-REF>
    <POLICY-REF about="/P3P/Policies.xml#second">
       <COOKIE-INCLUDE name="obnoxious-cookie" value="*" domain=".example.com" path="/"/>
    </POLICY-REF>
 </POLICY-REFERENCES>
</META>

[15]

cookie-include

"<COOKIE-INCLUDE"
   [` name="` token `"`]   ; matches the cookie's NAME
   [` value="` token `"`]  ; matches the cookie's VALUE
   [` domain="` token `"`] ; matches the cookie's Domain
   [` path="` token `"`]   ; matches the cookie's Path
"/>"

[16]

cookie-exclude

"<COOKIE-EXCLUDE"
   [` name="` token `"`]   ; matches the cookie's NAME
   [` value="` token `"`]  ; matches the cookie's VALUE
   [` domain="` token `"`] ; matches the cookie's Domain
   [` path="` token `"`]   ; matches the cookie's Path
"/>"

Here, token, NAME, VALUE, Domain and Path are defined as per RFC 2965 [STATE], with the addition that the '*' character is to be treated as a wildcard, as defined in section 2.3.2.1.2.

Note that [STATE] states default values for the domain and path attributes of cookies: these should be used in the comparison if those attributes are not found in a specific cookie. Also, conforming to [STATE], if an explicitly specified Domain value does not start with a full stop ("."), the user agent MUST prepend a full stop for it; and, note that every Path begins with the "/" symbol.

2.3.2.8 The `METHOD` element

By default, a policy reference applies to the stated URIs regardless of the method used to access the resource. However, a Web site may wish to define different P3P policies depending on the method to be applied to a resource. For example, a site may wish to collect more data from users when they are performing PUT or DELETE methods than when performing GET methods.

The METHOD element in a policy reference file is used to state that the enclosing policy reference only applies when the specified methods are used to access the referenced resources. The METHOD element may be repeated to indicate multiple applicable methods. If the METHOD element is not present in a POLICY-REF element, then that POLICY-REF element covers the resources indicated regardless of the method used to access them.

So, to state that /P3P/Policies.xml#first applies to all documents in the subtree /docs/ for GET and HEAD methods, while /P3P/Policies.xml#second applies for PUT and DELETE methods, the following policy reference would be written:

Example 2.6:

<META xmlns="http://www.w3.org/2001/09/P3Pv1">
 <POLICY-REFERENCES>
    <POLICY-REF about="/P3P/Policies.xml#first">
      <INCLUDE>/docs/*</INCLUDE>
      <METHOD>GET</METHOD>
      <METHOD>HEAD</METHOD>
    </POLICY-REF>
    <POLICY-REF about="/P3P/Policies.xml#second">
      <INCLUDE>/docs/*</INCLUDE>
      <METHOD>PUT</METHOD>
      <METHOD>DELETE</METHOD>
    </POLICY-REF>
 </POLICY-REFERENCES>
</META>

Note that HTTP requires the same behavior for GET and HEAD requests, thus it is inappropriate to specify different P3P policies for these methods. The syntax for the METHOD element is:

[17]	method-element	=	`<METHOD>` Method `</METHOD>`
Here, `Method` is defined in the section 5.1.1 of [HTTP1.1].

Finally, note that the METHOD element is designed to be used in conjunction with INCLUDE or COOKIE-INCLUDE elements. A METHOD element by itself will never apply a POLICY-REF to a URI.

2.3.3 Applying a Policy to a URI

A policy reference file specifies the policy which applies to a given URI. The meaning of this is that the indicated policy describes all effects of performing any of the methods listed in the policy reference file against the given URI.

There is a general rule which describes what it means for a P3P policy to cover a URI: the referenced policy MUST cover actions that the user's client software is expected to perform as a result of requesting that URI. Obviously, the policy must describe all data collection performed by site as a result of processing the request for the URI. Thus, if a given URI is covered for terms of GET requests, then the policy given by the policy reference file MUST describe all data collection performed by the site when that URI is fetched. Likewise, if a URI is covered for POST requests, then any data collection that occurs as a result of posting a form or other content to that URI MUST be described by the policy.

The concept of "actions that the client software is expected to perform" includes the setting of client-side cookies or other state-management mechanisms invoked by the response. If executable code is returned when a URI is requested, then the P3P policy covering that URI MUST cover certain actions which will occur when that code is executed. The covered actions are any actions which could take place without the user explicitly invoking them. If explicit user action causes data to be collected, then the P3P policy covering the URI for that action would disclose that data collection.

Some specific examples:

Fetching a URI returns an HTML page which contains a form, and the form contents are sent to a second URI when the user clicks a "Submit" button. The P3P policy covering the second URI MUST disclose all data collected by the form. The P3P policy covering the first URI (the URI the form was loaded from) MAY or MAY NOT disclose any of the data that will be collected on the form.
An HTML page includes JavaScript code which tracks how long the page is displayed and whether the user moved the mouse over a certain object on the page; when the page is unloaded, the JavaScript code sends that information to the server where the HTML page originated. The activity of the JavaScript code MUST be covered by the P3P policy of the HTML page. The reasoning is that this activity takes place without the user's knowledge or consent, and it occurs automatically as a result of loading the page.
A response is an installable image for an electronic mail program. In order to use the email program, the user must run an installation program, start the email program, and use its facilities. The P3P policy covering URI from where the email program was downloaded is not required to make a statement about the data which could be collected by using the email program. Installing and running the email program is clearly outside the Web browsing experience, so it is not covered by this specification. A separate protocol could be designed to allow downloaded applications to present a P3P policy, but this is outside the scope of this specification.
An HTML page containing a form includes a reference to an executable which provides a custom client-side control. The data in the control is submitted to a site when the form is submitted. In this case, the URI for the HTML page and the URI for the custom control is not required to make a statement about the data the custom control represents. However, the URI to which the form contents are posted MUST cover the data from the custom control, just as it would cover any other data collected by processing the form. This behavior is similar to the way HTML forms are handled when they use only standard HTML controls: the control itself collects no data, and the data is collected when the form is posted. Note that this example assumes that the form is only posted when the user actively presses a "submit" or similar button. If the form were posted automatically (for example, by some JavaScript code in the page), then this example would be similar to example #2, and the data collected by the form MUST be described in the P3P policy which covers the HTML form.
Requests to a URI are redirected to a third party. If the first party embeds previously collected personal data in the query string or other part of the redirect URI, the privacy policy for the first party's URI MUST describe the types of data transmitted and include the third party as a recipient.

2.3.4 Forms and Related Mechanisms

Forms deserve special consideration, as they often link to CGI scripts or other server-side applications in their action URIs. It is often the case that those action URIs are covered by a different policy than the form itself.

If a user agent is unable to find a matching include-rule for a given action URI in the policy reference file that was referenced from the page, it SHOULD assume that no policy is in effect. Under these circumstances, user agents SHOULD check the well-known location on the host of the action URI to attempt to find a policy reference file that covers the action URI. If this does not provide a P3P policy to cover the action URI, then a user agent MAY try to retrieve the policy reference file by using the HINT mechanism on the action URI, and/or by issuing a HEAD request to the action URI before actually submitting any data in order to find the policy in effect. Services SHOULD ensure that server-side applications can properly respond to such HEAD requests and return the corresponding policy reference link in the headers. In case the underlying application does not understand the HEAD request and no policy has been predeclared for the action URI in question, user agents MUST assume that no policy is in effect and SHOULD inform the user about this or take the corresponding actions according to the user's preferences.

Note that services might want to make use of the <METHOD> element in order to declare policies for server-side applications that only cover a subset of supported methods, e.g., POST or GET. Under such circumstances, it is acceptable that the application in question only supports the methods given in the policy reference file (i.e., HEAD requests need not be supported). User agents SHOULD NOT attempt to issue a HEAD request to an action URI if the relevant methods specified in the form's method attribute have been properly predeclared in the page's policy reference file.

In some cases, different data is collected at the same action URI depending on some selection in the form. For example, a search service might offer to both search for people (by name and/or email) and (arbitrary) images. Using a set of radio buttons on the form, a single server-side application located at one and the same action URI handles both cases and collects the required information necessary for the search. If a service wants to predeclare the data collection practices of the server-side application it MAY declare all of the data collection practices in a single policy file (using a <INCLUDE> declaration matching the action URI). In this case, user agents MUST assume that all data elements are collected under every circumstance. This solution offers the convenience of a single policy but might not properly reflect the fact that only parts of the listed data elements are collected at a time. Services SHOULD make sure that a simple HEAD request to the action URI (i.e., without any arguments, especially without the value of the selected radio button) will return a policy that covers all cases.

Note that if a form is handled through use of the GET method, then the action URI reflects the choice of form elements selected by the user. In some cases, it will be possible to make use of the wildcard syntax allowed in policy reference files to specify different policies for different uses of the same form action-handler URI. Therefore, user agents MUST include the query-string portion of URIs when making comparisons with INCLUDE and EXCLUDE elements in policy reference files.

2.4 Additional Requirements

2.4.1 Non-ambiguity

User agents need to be able to determine unambiguously what policy applies to a given URI. Therefore, sites SHOULD avoid declaring more than one non-expired policy for a given URI. In some rare case sites MAY declare more than one non-expired policy for a given URI, for example, during a transition period when the site is changing its policy. In those cases, the site will probably not be able to determine reliably which policy any given user has seen, and thus it MUST honor all policies (this is also the case for compact policies, cf. Section 4.1 and Section 4.6). Sites MUST be cautious in their practices when they declare multiple policies for a given URI, and ensure that they can actually honor all policies simultaneously.

If a policy reference file at the well-known location declares a non-expired policy for a given URI, this policy applies, regardless of any conflicting policy reference files referenced through HTTP headers or HTML link tags.

If an HTTP response includes references to more than one policy reference file, P3P user agents MUST ignore all references after the first one.

If an HTML file includes HTML link tag references to more than one policy reference file, P3P user agents MUST ignore all references after the first one.

If a user agent discovers more than one non-expired P3P policy for a given URI (for example because a page has both a P3P header and a link tag that reference different policy reference files, or because P3P headers for two pages on the site reference different policy reference files that declare different policies for the same URI), the user agent MAY assume any (or all) of these policies apply as the site MUST honor all of them.

2.4.2 Multiple Languages

Multiple language versions (translations) of the same policy can be offered by the server using the HTTP "Content-Language" header to properly indicate that a particular language has been used for the policy. This is useful so that human-readable fields such as entity and consequence can be presented in multiple languages. The same mechanism can also be used to offer multiple language versions for data schemas.

Whenever Content-Language is used to distinguish policies at the same URI that are offered in multiple languages, the policies MUST have the same meaning in each language. Two policies (or two data schemas) are taken to be identical if

All formal (not natural language) protocol elements are semantically identical (i.e., attribute order does not matter, the presence or absence of a default value does not matter, but attribute values matter)
All natural language protocol elements correspond one-to-one, and for each correspondence, one is a careful translation of the other.

Due to the use of the Accept-Language mechanism, implementers should take note that user agents may see different language versions of a policy or policy reference file despite sending the same Accept-Language request header if a new language version of a policy or data schema has been added.

2.4.3 The "Safe Zone"

P3P defines a special set of "safe zone" practices, which SHOULD be used by all P3P-enabled user agents and services for the communications which take place as part of fetching a P3P policy or policy reference file. In particular, requests to the well-known location for policy reference files SHOULD be covered by these "safe zone" practices. Communications covered by the safe zone practices SHOULD have only minimal data collection, and any data that is collected is used only in non-identifiable ways.

To support this safe zone, P3P user agents SHOULD suppress the transmission of data unnecessary for the purpose of finding a site's policy until the policy has been fetched. Therefore safe-zone practices for user agents include the following requirements:

User agents SHOULD NOT send the HTTP Referer header in the safe zone
User agents SHOULD NOT accept cookies from safe-zone requests
User agents MAY also wish to refrain from sending user agent information or cookies accepted in a previous session on safe zone requests
User agent implementers need to be aware that there is a privacy trade-off with using the Accept-Language HTTP header in the safe zone. Sending the correct Accept-Language header will allow fetching a P3P policy in the user's preferred natural language (if available), but does expose a certain amount of information about the identity of the user. User agents MAY wish to allow users to decide when these headers should be sent.

Safe-zone practices for servers include the following requirements:

Servers SHOULD NOT require the receipt of an HTTP Referer header, cookies, user agent information, or other information unnecessary for responding to requests in the safe zone
If the communications is taking place over a secure connection (such as SSL), then the server SHOULD NOT require an identity certificate from the user agent for safe zone requests
In addition, servers SHOULD NOT use in an identifiable way any information collected while serving a safe zone request

Note that the safe zone requirements do not say that sites cannot keep identifiable information -- only that they SHOULD NOT use in an identifiable way any information collected while serving a policy file. Tracking down the source of a denial of service attack, for example, would be a legitimate reason to use this information and ignore this recommendation.

2.4.4 Non-Discrimination of Policies

Servers SHOULD make every effort to help user agents find P3P policies. In particular, servers SHOULD place a policy reference file at the well-known location whenever possible. When the P3P HTTP header is used as an alternative, servers SHOULD:

Reference a policy in response to any request:: P3P-compliant sites SHOULD include a link to a policy reference file for a Webresource whenever possible.
Support HTTP HEAD requests: P3P-compliant servers SHOULD support HEAD requests for any documents that can be retrieved with GET requests. Whenever technically feasible, servers should give a valid response to a HEAD request for documents that are normally accessed by other HTTP methods as well (such as POST).

2.4.5 Security of Policy Transport

P3P policies and references to P3P policies SHOULD NOT, in themselves, contain any sensitive information. This means that there are no additional security requirements for transporting a reference to a P3P policy beyond the requirements of the document it is associated with; so, if an HTML document would normally be served over a non-encrypted session, then the P3P protocol would not require nor recommend that the document be served over an encrypted session when a reference to a P3P policy is included with that document.

2.4.6 Policy Updates

Note that when a Web site changes its P3P policy, the old policy applies to data collected when it was in effect. It is the responsibility of the site to keep records of past P3P policies and policy reference files along with the dates when they were in effect, and to apply these policies appropriately.

If a site wishes to apply a new P3P policy to previously collected data, it MUST provide appropriate notice and opportunities for users to accept the new policy that are consistent with applicable laws, industry guidelines, or other privacy-related agreements the site has made.

2.4.7 Absence of Policy Reference File

If no policy reference file is available for a given site, user agents MUST assume (an empty) policy reference file exists at the well-known location with a 24 hour expiry, and therefore if the user returns to the site after 24 hours, the user agent MUST attempt to fetch a policy reference file from the well-known location again. User agents MAY check the well-known location more frequently, or upon a certain event such as the user clicking a browser refresh button. Sites MAY place a policy reference file at the well-known location that indicates that no policy is available, but set the expiry such that user agents know they need not check every 24 hours.

2.4.8 Asynchronous Evaluation

User agents MAY asynchronously fetch and evaluate P3P policies. That is, P3P policies need not necessarily be fetched and evaluated prior to other HTTP transactions.This behavior may be dependent on the the user's preferences and the type of request being made. Until a policy is evaluated, the user agent SHOULD treat the site as if it has no privacy policy. Once the policy has been evaluated, the user agent SHOULD apply the user's preferences. To promote deterministic behavior, the user agent SHOULD defer application of a policy until a consistent point in time. For example, a web browser might apply a user's preferences just after the user agent completes a navigation, or when confirming a form submission.

2.5 Example Scenarios

As an aid to sites deploying P3P, several example scenarios are presented, along with descriptions of how P3P is used on those sites.

Scenario 1: Web site basic.example.com uses a variety of images, all of which it hosts. It also includes some forms, which are all submitted directly to the site. This site can declare a single P3P policy for the entire site (or if different privacy policies apply to different parts of the site, it can declare multiple P3P policies). As long as all of the images and form action URIs are in directories covered by the site's P3P policy, user agents will automatically recognize the images and forms as covered by the site's policy.

Scenario 2: Web site busy.example.com uses a content distribution network called cdn.example.com to host its images so as to reduce the load on its servers. Thus, all of the images on the site have URIs at cdn.example.com. CDN acts as an agent to Busy in this situation, and collects no data other than log data. This log data is used only for Web site and system administration in support of providing the services that Busy contracted for. Busy's privacy policy applies to the images hosted by CDN, so Busy uses the HINT element in its policy reference file to point to a suitable policy reference file at CDN, indicating that such images are covered by example.com P3P policy.

Scenario 3: Web site busy.example.com also has a contract with an advertising company called clickads.example.com to provide banner ads on its site. The contract allows Clickads to set cookies so as to make sure each user doesn't see a given ad more than three times. Clickads collects statistics on how many users view each ad and reports them to the companies whose products are being advertised. But these reports do not reveal information about any individual users. As was the case in Scenario 2, Busy's privacy policies applies to these ads hosted by Clickads, so Busy uses the HINT element in its policy reference file to point to a suitable policy reference file at Clickads, indicating that Busy P3P policy applies to such embedded content served by clickads.example.com. The companies whose products are being advertised need not be mentioned in the Busy privacy policy because the only data they are receiving is aggregate data.

Scenario 4: Web site busy.example.com also has a contract with funchat.example.com to host a chat room for its users. When users enter the chat room they are actually leaving the Busy site. However, the chat room has the Busy logo and is actually covered by the Busy privacy policy. In this instance Funchat is acting as an agent for Busy, but -- unlike the previous examples -- their content is not embedded in the Busy site. Busy can use the HINT element in its policy reference file to point to a suitable Funchat policy reference file, that indicates that Funchat chat room is covered by Busy privacy policy, therefore facilitating a smoother transition to the chat room.

Scenario 5: Web site bigsearch.example.com has a form that allows users to type in a search query and have it performed on their choice of search engines located on other sites. When a user clicks the "submit" button, the search query is actually submitted directly to these search engines -- the action URI is not on bigsearch.example.com but rather on the search engine selected by the user. Bigsearch can declare the privacy policies for these search engines by using the HINT element to point to their corresponding policy reference files. So when a user clicks the "submit" button, their user agent can check its privacy policy before posting any data. In order to make this search choice mechanism work, Bigsearch might actually have a form with an action URI on its own site, which redirects to the appropriate search engine. In this case, the user agent should check the search engine privacy policy upon receiving the redirect response.

Scenario 6: Web site bigsearch.example.com also has a form that allows users to type in a search query and have it simultaneously performed on ten different search engines. Bigsearch submits the queries, gets back the results from each search engine, removes the duplicates, and presents the results to the user. In this case, the user interacts only with Bigsearch. Thus, the only P3P policy involved is the one that covers the Bigsearch Web site. However, Bigsearch must disclose that it shares the users' search queries with third parties (the search Web sites), unless Bigsearch has a contract with these search engines and they act as agents to Bigsearch.

Scenario 7: Web site bigsearch.example.com also has banner advertisements provided by a company called adnetwork.example.com. Adnetwork uses cookies to develop profiles of users across many different Web sites so that it can provide them with ads better suited to their interests. Because the data about the sites that users are visiting is being used for purposes other than just serving ads on the Bigsearch Web site, Adnetwork cannot be considered an agent in this context. Adnetwork must create its own P3P policy and use its own policy reference file to indicate what content it applies to. In addition, Bigsearch may optionally use the HINT element in its policy reference file to indicate that the Adnetwork P3P policy reference file applies to these advertisements. Bigsearch should only do this if Adnetwork has told it what P3P policy applies to these advertisements and has agreed to notify Bigsearch if the policy reference needs to be changed.

Scenario 8: Web site busy.example.com uses cookies throughout its web site. It discloses a cookie policy, separate from its regular P3P policy to cover these cookies. It uses the COOKIE-INCLUDE element in its policy reference file to declare the appropriate policy for these cookies. As a performance optimization, it also makes available a compact policy by sending a P3P header that includes this compact policy whenever it sets a cookie.

Scenario 9: Web site config.example.com provides a service in which they optimize various kinds of web content based on each user's computer and Internet configuration. Users go to the Config web site and answer questions about their computer, monitor, and Internet connection. Config encodes the responses and stores them in a cookie. Later, when the user is visiting Busy -- a web site that has contracted with Config -- whenever the browser requests content that can be optimized (certain images, audio files, etc.), Busy will redirect the user to Config, which will read the user's cookie, and deliver the appropriate content. In this case, Config should declare a privacy policy that describes the kinds of data collected and stored in its cookies, and how that data is used. It should use a COOKIE-INCLUDE element in its policy reference file to declare the policy for the cookies. It will probably reference Busy's P3P policy for the actual images or audio files delivered, as it is acting much like CDN acts in scenario 2. Busy will probably also use HINT elements in its policy reference file to reference the policy for the Config-delivered content.

3. Policy Syntax and Semantics

P3P policies are encoded in XML. They may also be represented using the RDF data model ([RDF]); however, an RDF representation is not included in this specification. (Such a representation is planned to be made available as a W3C Note prior to submitting P3P as a Proposed Recommendation, together with a suitable RDF encoding of the policy reference file).

Section 3.1 begins with an example of an English language privacy policy and a corresponding P3P policy. P3P policies include general assertions that apply to the entire policy as well as specific assertions -- called statements -- that apply only to the handling of particular types of data referred to by data references. Section 3.2 describes the POLICY element and policy-level assertions. Section 3.3 describes statements and data references.

3.1 Example policies

3.1.1 English language policies

The following are two examples of English-language privacy policy to be encoded as a P3P policy. Both policies are for one example company, CatalogExample, which has different policies for those browsing their site and those actually purchasing products. Example 3.1. is provided in both English and as a more formal description using P3P element and attribute names.

Example 3.1: CatalogExample's Privacy Policy for Browsers

At CatalogExample, we care about your privacy. When you come to our site to look for an item, we will only use this information to improve our site and will not store it with information we could use to identify you.

CatalogExample, Inc. is a licensee of the PrivacySealExample Program. The PrivacySealExample Program ensures your privacy by holding Web site licensees to high privacy standards and confirming with independent auditors that these information practices are being followed.

Questions regarding this statement should be directed to:

CatalogExample

      4000 Lincoln Ave.

      Birmingham, MI 48009 USA

      email: catalog@example.com

      Telephone 248-EXAMPLE (248-392-6753)

If we have not responded to your inquiry or your inquiry has not been satisfactorily addressed, you can contact PrivacySealExample at http://www.privacyseal.example.org. CatalogExample will correct all errors or wrongful actions arising in connection with the privacy policy.

What We Collect and Why:
When you browse through our site we collect:

the basic information about your computer and connection to make sure that we can get you the proper information and for security purposes.
aggregate information on what pages consumers access or visit to improve our site.

Data retention:
We purge every two weeks the browsing information that we collect.

Here is Example 3.1 in a more formal description, using the P3P element and attribute names [with the section of the spec that was used cited in brackets for easy reference]:

Disclosure URI: http://www.catalog.example.com/PrivacyPracticeBrowsing.html
[3.2.2 Policy]
Entity: CatalogExample
4000 Lincoln Ave.
Birmingham, MI 48009
USA
catalog@example.com
+1 (248) 392-6753
[3.2.4 Entity]
Access to Identifiable Information: None
[3.2.5 Access]
Disputes:
resolution type: independent
service: http://www.privacyseal.example.org
description: PrivacySealExample
[3.2.6 Disputes]
Remedies: we'll correct any harm done wrong
[3.2.7 Remedies]
We collect:
dynamic.clickstream
dynamic.http
[4.5 Base data schema]
For purpose: Web site and system administration, research and development
[3.3.4 Purpose]
Recipients: Only ourselves and our agents
[3.3.5 Recipients]
Retention: As long as appropriate for the stated purposes
[3.3.6 Retention]
(Note also that the site's human-readable privacy policy MUST mention that data is purged every two weeks, or provide a link to this information.)

Example 3.2: CatalogExample's Privacy Policy for Shoppers

At CatalogExample, we care about your privacy. We will never share your credit card number or any other financial information with any third party. With your permission only, we will share information with carefully selected marketing partners that meet either the preferences that you've specifically provided or your past purchasing habits. The more we and know about your likes and dislikes, the better we can tailor offerings to your needs.

CatalogExample is a licensee of the PrivacySealExample Program. The PrivacySealExample Program ensures your privacy by holding Web site licensees to high privacy standards and confirming with independent auditors that these information practices are being followed.

Questions regarding this statement should be directed to:

CatalogExample

      4000 Lincoln Ave.

      Birmingham, MI 48009 USA

      email: catalog@example.com

      Telephone +1 248-EXAMPLE (+1 248-392-6753)

If we have not responded to your inquiry or your inquiry has not been satisfactorily addressed, you can contact PrivacySealExample - http://privacyseal.example.org/privacyseal. CatalogExample will correct all errors or wrongful actions arising in connection with the privacy policy.

When you browse through our site we collect:

the basic information about your computer and connection to make sure that we can get you the proper information and for security purposes; and
aggregate information on what pages consumers access or visit to improve our site

If you choose to purchase an item we will ask you for more information including:

your name and address so that we can have your purchase delivered to you and so we can contact you in the future;
your email address and telephone number so we can contact you;
a login and password to use to update your information at any time in the future; and
financial information to complete your purchase (you may choose to store this for future use)
optionally, you can enter other demographic information so that we can tailor services to you in the future.

Also on this page we will give you the option to choose if you would like to receive email, telephone calls or written service from CatalogExample or from our carefully selected marketing partners who maintain similar privacy practices. If you would like to receive these solicitations simply check the appropriate boxes. You can choose to stop participating at any time simply by changing your preferences.

Changing and Updating personal information
Consumers can change all of their personal account information by going to the preferences section of CatalogExample at http://catalog.example.com/preferences.html. You can change your address, telephone number, email address, password as well as your privacy settings.

Cookies
CatalogExample uses cookies only to see if you have been an CatalogExample customer in the past and, if so, customize services based on your past browsing habits and purchases. We do not store any personal data in the cookie nor do we share or sell the any of the information with other parties or affiliates.

Data retention
We will keep the information about you and your purchases for as long as you remain our customer. If you do not place an order from us for one year we will remove your information from our databases.

3.1.2 XML encoding of policies

The following pieces of [XML] capture the information as expressed in the above two examples. P3P policies are statements that are properly expressed as well-formed XML. The policy syntax will be explained in more detail in the sections that follow.

XML Encoding of Example 3.1:

 <POLICY name="forBrowsers" 
     discuri="http://www.catalog.example.com/PrivacyPracticeBrowsing.html">
  <ENTITY>
   <DATA-GROUP>
    <DATA ref="#business.name">CatalogExample</DATA>
    <DATA ref="#business.contact-info.postal.street">4000 Lincoln Ave.</DATA>
    <DATA ref="#business.contact-info.postal.city">Birmingham</DATA>
    <DATA ref="#business.contact-info.postal.stateprov">MI</DATA>
    <DATA ref="#business.contact-info.postal.postalcode">48009</DATA>
    <DATA ref="#business.contact-info.postal.country">USA</DATA>
    <DATA ref="#business.contact-info.online.email">catalog@example.com</DATA>
    <DATA ref="#business.contact-info.telecom.telephone.intcode">1</DATA>
    <DATA ref="#business.contact-i