The Web borrows familiar concepts from physical media (the notion of a "page," for example) and overlays them on top of a networked infrastructure (the Internet) and digital presentation medium (the browser software). This is a convenient abstraction, but when social or legal concepts and frameworks relating documents, publishing and speech are applied to the Web, the analogies often do not suffice. Publishing a page on the Web is fundamentally different from printing and distributing a page in a magazine or book.
Telecommunication is often subject to governance: legislation, legal opinion, regulation, convention and contract -- ways in which society looks to enforce norms, for example, around copyright, censorship, privacy and other areas. But there is often a mismatch between governance intended to apply to the Web (usually based on the analogy with physical media) and the technology and architecture used to create it.
This document is intended to inform future social and legal discussions of the Web by clarifying the ways in which the Web's technical facilities operate to store, publish and retrieve information, and by providing definitions for terminology as used within the Web's technical community. This document also describes the technical and operational impact that does or could result from legal constraints on publishing, linking and transformation on the Web.
One particular mismatch between the Web and physical media is the way in which publication can happen without any judgment or review by Web subsystems based on actions of end-users, either by web intermediaries such as proxies, archives, search engines, or by content transformation services. Such sub-systems cannot exercise judgment, even if required to by governance. This document also discusses possible technical mechanisms for indicating desired constraints on the use of material that is published on the web, including its indexing, embedding and transformation, which might aid in accomplishing the goals of intended governance effectively.
This is an Editor's Draft which the TAG intends to become a Working Draft on the Recommendation track at W3C.
The act of viewing a web page is a complex interaction between a user's browser and any number of web servers. Unlike reading a book, viewing a web page involves copying the data held on the servers onto the user's computer. Logic encoded within the page may cause more copying to take place — of images, videos and other files, perhaps from other servers, that are displayed or otherwise used within the original page — often without the user's explicit knowledge or consent. For an end user, it is usually impossible to tell whether a given image or video displayed within a page originates from the server the page comes from or from some other location.
Proxy servers and services that combine and repackage data from other sources may also retain copies of this material. These intermediary services may transform, translate or rewrite some of the material that passes through them, to enhance the user's experience of the web page.
Still other services on the web, such as search engines and archives, make copies of content as a matter of course. This is in part to facilitate the indexing necessary to their operation, and in part to enable presentation of search results, to provide value to their users and to the original authors of the web page.
Licenses that describe how material may be copied and altered by others tend not to distinguish between a proxy compressing a web page to make it load faster and someone editing and republishing the page on their own website. To illustrate, the Creative Commons Attribution-NoDerivs defines the terms (emphasis added):
- means a work based upon the Work, or upon the Work and other pre-existing works, such as a translation, adaptation, derivative work, arrangement of music or other alterations of a literary or artistic work, or phonogram or performance and includes cinematographic adaptations or any other form in which the Work may be recast, transformed, or adapted including in any form recognizably derived from the original, except that a work that constitutes a Collection will not be considered an Adaptation for the purpose of this License. For the avoidance of doubt, where the Work is a musical work, performance or phonogram, the synchronization of the Work in timed-relation with a moving image ("synching") will be considered an Adaptation for the purpose of this License.
- means to make available to the public the original and copies of the Work through sale or other transfer of ownership.
- means to make copies of the Work by any means including without limitation by sound or visual recordings and the right of fixation and reproducing fixations of the Work, including storage of a protected performance or phonogram in digital form or other electronic medium.
Consider the following questions:
Terms and Conditions statements on websites also list acceptable and unacceptable behaviour on a site, with any browsing on the site implicitly indicating acceptance of the terms. These generally do not take into account the behaviour of proxies. For instance, one standard set of terms and conditions includes:
You must not:
(a) republish material from this website (including republication on another website);
(b) sell, rent or sub-license material from the website;
(c) show any material from the website in public;
(d) reproduce, duplicate, copy or otherwise exploit material on our website for a commercial purpose;
(e) edit or otherwise modify any material on the website; or
(f) redistribute material from this website except for content specifically and expressly made available for redistribution (such as our newsletter)
It is not possible to view material on the web without it being downloaded onto your computer, so forbidding downloading except for caching purposes essentially means that people cannot view the page. In addition, many proxies automatically transform the documents that pass through them, for example to compress them so that they take up less bandwidth for mobile consumption or to introduce adverts into pages that are accessed through "free" WiFi.
Limits placed on the use of a website often include limitations on automatic indexing of the website, without exceptions for the search engines that make the website discoverable or the archives that ensure its longevity. For example, the same set of terms and conditions as described above includes:
You must not conduct any systematic or automated data collection activities (including without limitation scraping, data mining, data extraction and data harvesting) on or in relation to our website without our express written consent.
Search engines rely on systematic data collection from websites in order to provide their users with accurate search results, and archives similarly in order to retain websites for posterity. So, these terms and conditions, if adhered to, effectively render any website that uses them undiscoverable. But automated agents — spiders and robots — that gather information from the web are unable to read these terms; the only things they understand are the technical signals that a website provides about what is permitted.
As another example, the terms and conditions for gsig.com include:
Use of Materials: Upon your agreement to the Terms, GSI grants you the right to view the site and to download materials from this site for your personal, non-commercial use. You are not authorized to use the materials for any other purpose. If you do download or otherwise reproduce the materials from this Site, you must reproduce all of GSI’s proprietary markings, such as copyright and trademark notices, in the same form and manner as the original.
You may not use any “deep-link”, “page-scrape”, “robot”, “spider” or any other automatic device, program, algorithm or methodology or any similar or equivalent manual process to access, acquire, copy or monitor any portion of the Site or any of its content, or in any way reproduce or circumvent the navigational structure or presentation of the Site.
However, the site does not use the primary technical method of actually controlling what spiders or robots access on the site, namely a
Many sites have a linking policy that limits what links can be made to the site from other sites; that these policies are directly accessible through searches for "all links should point to" illustrates that these conditions are not backed up through technical mechanisms that would prevent such links from being made. For example, the website at quotec.co.uk has a linking policy that includes:
Links pointing to this website should not be misleading.
Appropriate link text should be always be used.
From time to time we may update the URL structure of our website, and unless we agree in writing otherwise, all links should point to http://www.quotec.co.uk.
You must not use our logo to link to this website (or otherwise) without our express written permission.
You must not link to this website using any inline linking technique.
You must not frame the content of this website or use any similar technology in relation to the content of this website.
Legislation that governs the possession and distribution of unlawful material (such as child pornography, information that is under copyright or material that is legally suppressed through a gag order) often needs to exempt certain types of services, such as caching or hosting, as it would be impractical for the people running those services to police all the material that passes through their servers. An example of legislation that does this in the UK is the Coroners and Justice Act 2009 Schedule 13; from the Explanatory Notes (emphasis added):
Paragraphs 3 to 5 of [Schedule 13] provide exemptions for internet service providers from the offence of possession of prohibited images of children in limited circumstances, such as where they are acting as mere conduits for such material or are storing it as caches or hosts.
Examples of the kind of legal questions that have arisen are:
There are many other examples on the Wikipedia page on Copyright aspects of hyperlinking and framing.
This document does not aim to address whether particular activities on the web are illegal or legal; this is outside the scope of the TAG. Instead, it aims to:
This section summarises the terminology that is used within this paper. More details about each of the terms is given in the rest of the document.
The concept of publishing on the web has evolved as the web's ecosystem has enlarged and diversified, and as the capabilities of browsers and the web standards that they implement have developed. There is no single definition of what publishing on the web means. Instead there are a number of activities that could be viewed as publication or distribution in a legal sense, or something else. This section describes each of these activities and how they work.
The basic form of publication on the web is hosting. A server hosts a file if it stores the file on disk or generates the file from data that it stores, and that file did not (to the server's knowledge) originate elsewhere on the web.
The presence of data on a server does not necessarily mean that the organisation that owns and maintains the server has an awareness of the presence of the data or its content. Many websites are hosted on shared hardware that is owned by a service provider that stores and serves data at the direction of controlling individuals and organisations which determine the data they provide on the site. Because of this, multiple servers may host the same file at different URIs. For example, an artist could upload the same image to multiple servers, which then store the image and serve it to others.
There are many different types of service provider. Some may exercise practically no control over the software and data that they host, merely providing a base platform on which code can run. Others may focus on particular types of content, such as images (eg Flickr), videos (e.g. YouTube) or messages (e.g. Twitter). Also, there may be many service providers involved in the publication of a particular file on the web: some providing hardware, others providing different kinds of publishing support.
Some service providers automatically perform transformations on material that they host, as a service, such as converting to alternative formats, clipping or resizing, or marking up text. When they sign up to a service, controllers explicitly or implicitly enter into an agreement with the service provider that grants them a license to perform transformations on the material which they upload.
Transformation of Unlawful Material
Service providers that host particular types of material often employ automatic filters to prevent the publication of unlawful material, but it is impossible for a service provider to detect and filter out everything that might be unlawful.
To add to the complexity of this area, it is possible for each of the following to be in different jurisdictions:
and be controlled by different laws and conventions.
Some servers provide access to files that are hosted elsewhere on the web: on an origin server that holds the original version of the file. These files might be stored on the server and provided again at a later time, in which case for the purposes of this document it is termed a caching server, or might simply pass through the server in response to a request, in which case for the purposes of this document it is termed a relaying server.
It is usually impossible to tell whether a server is providing a stored response or has made a new request to an origin server and is serving the results of that request. Servers commonly store the results of some requests and not others, acting as a caching server some of the time and as a relaying server the rest.
In both cases, the file the caching or relaying server provides may be different from the original file that was accessed from the origin server. For example:
Caching and relaying servers are extremely useful on the web. There are four main types of caching and relaying servers discussed here: proxies, archives, search engines and reusers. The distinctions between them are summarised in the table below.
|purpose||increase network performance||maintain historical record||locate relevant information||better understand information|
|refreshing||based on HTTP headers||never||variable||based on HTTP headers|
|retrieval||on demand||proactive||proactive||usually on demand|
|URI use||usually uses same URI||uses new URI||uses new URI||uses new URI|
Controlling Proxy Behaviour
Proxies should comply with instructions from origin servers that describe whether pages may be copied and transformed, but will only be able to comply with those that are machine-readable.
Proxies come in four general flavors:
The use of a forward proxy, gateway or transforming proxy may be configured either on an individual machine or transparently for a particular network. Users may have no idea that their requests are channelled through a given proxy, or they may have configured their set-up to use the proxy.
Reverse proxies appear to be normal servers to users: it is impossible for a user to tell that their request is actually passed on to a completely different origin server, or where that server is. This is intentional as the origin server in this case is a private one.
To improve performance, some proxies, particularly CDNs, may pre-fetch resources that a page includes, since these resources are likely to be requested by the browser soon after the page is viewed. In other words, although generally the contents of a proxy's cache will be determined by the requests that users of that proxy have made, the proxy might also in some cases contain content that no one has ever requested.
Archives aim to catalog and provide access to some portion of web content to provide an on-going historical record. They use crawlers to fetch pages and other resources from the portion of the web that they cover, and store them on their own servers, along with some metadata about the pages, particularly when they were retrieved. They then may provide access to the stored copies of the resources at particular historical dates, enabling people to see how pages used to appear.
Controlling Archive Behaviour
Archives should comply with instructions from origin servers that describe whether pages may be copied and transformed, but will only be able to comply with those that are machine-readable.
Archives are usually run by institutions that have a legal mandate and responsibility to keep this historical record, such as a legal deposit. Although their primary purpose is long term record-keeping, they often make this material available online as well. They might restrict access to the data for a period of time after it is collected, for security or privacy reasons, and may respond to legally-backed removal requests. Users might use archives for research, but also to access information that has otherwise been removed from the Web.
When they are made available to the public, archived pages are usually distinguishable by end users from the original page using banners placed within the page or having the original page appear within a frame. The links (both to other pages and to embedded resources such as images) are usually rewritten so that when the user interacts with the page, they are taken to the version of the linked resource at the same point in time. "Dark archives" do not make their content available to the public.
Search engines aim to catalog and provide access to as many web pages as they can, so that they can direct users to appropriate information in response to a search. They use crawlers to fetch pages and other resources from the web, analyse them and store them on their own servers to support further analysis.
Controlling Search Engine Behaviour
Search engines should comply with instructions from origin servers that describe whether pages may be copied and transformed, but will only be able to comply with those that are machine-readable.
Search engines are most interested in indexing resources and providing links to them rather than in the content of the resource itself. They might not copy the page itself, but they always store metadata about the page, derived from the information in the page itself and other information on the web, such as what other pages link to it.
Search engines play an important role in the web in enabling people to find information, including that which would otherwise be lost or is temporarily unavailable. When a user views a stored page from a search engine, it is usually obvious both that the search engine is involved (from the URI of the page and from banners or framing), that the content originally came from somewhere else, and where it came from. The links within the page are not usually rewritten.
Data reuse is becoming more prevalent as web servers act as services to others. A server that is a reuser fetches information from one or more origin servers and either provides an alternative URI for the same page or adds value to it by reformatting it or combining it with other data. Good examples are the BBC Wildlife Finder, which incorporates information from Wikipedia, Animal Diversity Web and other sources or triplr.org, which converts RDF data from one format to another as a service.
Reusers should comply with instructions from origin servers that describe whether pages may be copied and transformed.
Attributing Reused Material
Reusers should indicate the sources of the information on pages, for both humans and computers.
Reusers that do not change the information from the origin server may be used to simplify access to the origin server (by mapping simple URLs to a more complex query) or to provide a route around gateways or the same-origin policy (as servers are not limited in where they access resources from).
Since reused information is, by design, seamlessly integrated into a page that is served from the reuser, people viewing that page will not generally be aware that the information originates from elsewhere. The URIs used for the pages will be those of the reuser, for example. Licenses on the material may require attribution; even when it doesn't, it is good practice for reusers to indicate where the material originates.
An alias is a URI that points the browser to another URI on an origin server. A server can automatically redirect a browser (using a HTTP
3XX status code and a
Location header). Web pages from a server can do the same thing using a
<meta> element with an
http-equiv attribute set to
Refresh; this technique is often used with a slight delay to indicate to the user that they are being redirected to another page.
Aliases do not involve any of the information from the origin server passing or being stored by the redirecting server, but the redirecting server will be able to record when a particular URI is requested.
Although it is preferable to only have one URI for a particular resource, redirections are a useful mechanism for managing change on the web. They are used within websites when the structure of the website changes, or between websites when a new website is created that supersedes the first, or to archived information when a host no longer wants to provide access to a file itself.
Redirections are also used to provide other services. Link shorteners provide a short URI for a resource that is then redirected to the original URI, and are useful in locations where space is limited such as in print or on Twitter. Depending on their implementation, link-tracking services can use a similar technique to enable servers to analyse which links are followed from their site: the link tracker records the request and redirects the user to the true target page.
When aliasing is used to provide a shorter alternative URI to a resource, best practice is to use a domain which is associated with the domain of the destination URI. This allows the end user to know more about where the link will send them and will potentially enhance the longevity of these aliases. Examples are nytim.es and bbc.in.
When aliasing is used, users may not be aware about the eventual target of a link, or the involvement of an aliasing server, both of which are important. Shortened links, for example, hide the target location behind a URI that often has no visible relationship to the eventual destination of the page. Some implementations of link tracking do not change the original destination of the link (such that the status bar on a browser shows the eventual target of the page) but instead use the
onclick event to direct the user to the aliasing server.
Following a redirection, browsers change the address bar to the new location, but this is often the only indication, and the user may miss it and be unaware of the redirection.
A web page written in HTML may include other resources, such as images, video, scripts, stylesheets, data and other HTML. The HTML in a web page refers to these external resources in markup, for example, an
<img> element uses the
src attribute to reference an image which should be shown within the page. Material that is included within a web page may appear to be a hosted copy to the user of a website, but in fact may be hosted completely separately, outside the control of the owner of the web page.
Includers should comply with computer and human-readable instructions from origin servers that describe whether and how resources may be included within a page.
Those who include third-party resources within their web pages should indicate the sources of the information on such page for both humans and computers.
HTML supports several different mechanisms for including other resources in a page. These are listed in , but they all work in basically the same way. Typically, when a user navigates to a web page, the browser automatically fetches all the included resources into its local cache and executes them or displays them within the page.
Inclusion is different from hosting, copying or disseminating a file because the information is never stored on, nor passes through, the server that hosts the web page doing the including. As such, although the included resources are an essential component of the page to make it appear and function as a whole, the server of the web page does not have control over their content which may change without the server's knowledge.
Users may not be aware that included resources are used within a page at all. When included resources are embedded within the page such that they are visible to a user, it may not be clear that an image or video is from a third-party website rather than the website that they are visiting unless this is explicitly indicated within the content of the page.
A resource that is included into a popular page causes a large number of requests to the server on which the file is published, which can be burdensome to the third-party who hosts the file. Publishers who intend their files to be reused in this way therefore typically have terms and conditions that apply to the reuse of those files and may have to put in place technical barriers to restrict it.
As with normal links, included resources may or may not have the same origin as the page that includes them. Resources such as images and scripts that are included within the web page may be from any site. However, browsers implement a same-origin policy which generally means that third-party resources cannot be fetched and processed by scripts running on the page, for example through XMLHttpRequests [[XMLHTTPREQUEST]] (though typically these scripts can write markup into the page which includes such resources).
When scripts or HTML are included into web pages, the included resource may itself include other resources (which may include still more and so on). The author of the original web page has control over which resources it includes, but does not have control over which resources those included resources go on to include. The publishers of included resources may change the content of those resources at any time, possibly without warning. This has been used in cases where websites included third-party images without permission, to substitute the image with something distasteful or to redirect to a link that performed an action on the user's behalf; see Preventing MySpace Hotlinking.
Some of the resources that are included within a page may be invisible to the user. An example is a hidden image that is used for tracking purposes: each time a user navigates to the page, the hidden image is requested; the server uses the information from the request of the image to build a picture of the visitors to the site.
This facility can be used for malicious purposes. An
<img> element can point to any URI (not just an image) and causes a GET request on that resource. If a website has been constructed such that GET requests cause an action to be carried out (such as logging out of a website), a page that includes this "image" will cause the action to take place.
Linking is a fundamental notion for the web. HTML pages use
<a> elements to insert links to other pages on the web, with the
href attribute holding the URI for the linked page. Some of the links will be to be pages from the same origin; others will be cross-origin links to pages on third-party's sites that hold related information.
Websites that seek to control how other websites link to them should use the technical mechanisms available to them rather than seek to restrict linking through terms and conditions.
A user can usually tell where a link is going to take them prior to selecting it through the browser UI (e.g. by "mousing over" it) or after the link is selected through the status bar in the browser, although some links are overridden by
onclick event handling that takes them to a different location. Some websites, such as Wikipedia, use icons to indicate when a link is a cross-origin link and when it will take a user to a page on the same server. The use of interstitial pages or dialog boxes which warn the user they are about to leave the site in question can obscure the eventual destination of the link, as discussed in .
If the link is a cross-origin link (or even in some cases where it is an internal link), the publisher of the origin page will have no control over the content or access policies of the linked page. These are the responsibility of the publisher of that page; the TAG Finding on "Deep Linking" in the World Wide Web [DEEPLINKING] describes the ways in which publishers can control access to their pages and the fundamental principle that addressing (linking to) a page is distinct from accessing it.
Traditionally, a user must take a specific action in order to navigate to the linked page, such as by clicking on the link or selecting it with a keystroke or a voice command. In these cases, the linked page cannot be accessed without the user's knowledge and consent (though they may not know where they will eventually end up).
There are three practices used by some sites that obscure whether a link is followed by the user.
prefetchlink relation in a link. For example, a page might indicate that the first result in a list of search results should be fetched before the user actually navigates the link.
The description above about how information is published on the web highlights how hard it can be for end users (both human and machine) to be aware of the original source of content on the web, and the ways in which it may have been changed en route to them. It also shows that the controllers of content need to be clear about how that content can be used elsewhere, both through human-readable prose and by the technical barriers that they put up that limit access. Third parties that use that content, whether proxies, reusers or linkers, should also follow some best practices in transformation, reuse and links to information.
Once material is put on the public web (that is, on the internet and unprotected by authentication barriers), it is impossible to completely limit how that material is used through technical means — HTTP headers can be faked, metadata can be ignored. However, there are a number of standard techniques that controllers can use to indicate how they intend their material to be used, which intermediate servers should pay attention to.
Publishers can control access to resources that are unprotected by authentication through HTTP, by refusing or redirecting connections to particular resources based on:
RefererHTTP header; this is useful for preventing linking to particular resources from outside a website, or preventing the inclusion of a resource in another website
User-AgentHTTP header; this is particularly useful for preventing access from crawlers
As well as the techniques above, which can be used to control any access to pages, it's also possible to provide additional control over the inclusion of resources in a third-party's web pages.
In the case of HTML pages, publishers can include a script that checks whether the document is the top document in the window, to prevent it from being embedded within a frame.
The Cross-Origin Resource Sharing Working Draft [[CORS]] defines a set of HTTP headers that can be used to give the publisher of the third-party resource greater control over access to their resources. These are usually used to open up cross-origin access to resources that publishers want to be reused, such as JSON or XML data exposed by APIs, by indicating to the browser that the resource can be fetched by a cross-origin script.
Embed-Only-From-Origin HTTP header is also currently under discussion by the Web Applications Working Group and described within the Cross-Origin Resource Embedding Restrictions Editor's Draft [CORER]. This would enable publishers to control which origins are able to embed the resources they publish into their pages.
Publishers should ensure actions are not taken on behalf of their users in response to an HTTP
GET on a URI, as otherwise sites are open to security breaches through inclusions, as described in . It is also good practice to check the
Referer header in these cases to prevent actions being taken as the result of the submission of forms within other website's web pages, unless that functionality is desired.
There are a number of HTTP headers [[HTTP11]] that enable content providers to indicate whether a proxy should cache a given page and for how long it should keep the copy. These are described in detail within Section 13: Caching in HTTP. For example, a server can use the HTTP header
Cache-Control: no-store to indicate that a particular resource should not be cached by a proxy server.
Publishers of websites can also indicate which pages should not be fetched or indexed by any search engine or archive through robots.txt [ROBOTS] and the robots
<meta> element [META]. They can indicate other characteristics of web pages, such as how frequently they might change and their importance on the website, through sitemaps [SITEMAPS]. More sophisticated publishers may use the Automated Content Access Protocol (ACAP) extensions [ACAP] to attempt to indicate access policies.
Publishers can also use the
rel="canonical" link relationship to indicate a canonical URI for a page which should be used by search engines and other reusers to reference a given page.
Cache-Control: no-transform HTTP header indicates that a proxy server must not change the original content, nor the headers:
For example, an proxy server must not convert a TIFF served with
Cache-Control: no-transform into a JPG, nor should it rewrite links within an HTML page.
One reason that people linking to websites use misleading links is when the original URLs are too long to incorporate into space-limited documents, such as short-form posts or in printed media. Although it's possible to use third-party link shortening services, origin websites can also set up link shorteners for their own content, and then use the
rel="shortlink" link relationship to point from the original page to the short link for that page.
Websites indicate a license that describes how the information within the website can be reused by others.
Just as with HTTP headers, robots.txt and sitemaps, there can be no technical guarantees that crawlers will honor license information within a site. However, to give well behaved crawlers a chance of identifying the license under which a page is published, websites should:
cc:licenseto indicate the license of included resources, such as images or videos
This section describes the techniques that you should use when operating a website that incorporates material from other sources, whether caching, transforming or simply linking.
As described in and , there are a number of HTTP headers and other conventions that indicate how an origin server intends other servers to treat the resources that they publish. Servers that cache or transform data from origin servers should obey these headers, which exist to ensure that the end user receives current information in the intended form.
Proxies must use the
Via HTTP header when they handle requests to origin servers, to indicate their involvement in the response to the user's original request. Proxies which perform transformations on a document must include a
Warning: 214 Transformation applied HTTP header in the response.
These and other recommendations for proxies which perform transformations are included in the Guidelines for Web Content Transformation Proxies 1.0.
Many licenses require the reusers of information to provide attribution to the original source of the material. This attribution must be human-readable, so that users of your website understand where the material came from, and may also be computer-readable, which enables automated tools to track the use of material on the web.
The wording and positioning of attribution is usually dictated by the license under which the material is made available. For example, the license for the free icons available from Axialis Software includes:
If you use the icons in your website, you must add the following link on each page containing the icons (at the bottom of the page for example):Icons by Axialis Team
The HTML code for this link is:<a href="http://www.axialis.com/free/icons">Icons</a> by <a href="http://www.axialis.com">Axialis Team</a>
If there is no explicit guidance about the location of attribution, it is recommended to include attribution to material from a third party as close to the use of that material as possible. Methods to make the attribution machine-readable include:
citeattribute on the
<blockquote>element, where a portion of a page is quoted within your own site
dc:sourceproperty with microformats, microdata or RDFa to indicate the source of a portion of the page (identified through an
An example of clear attribution of material from another site is that of the BBC Wildlife Finder; the following screenshot shows the attribution within the page on the Pygmy Three-toed Sloth.
There are a number of practices around linking to a third-party site that can help users and automated agents to understand the relationship between your website and the third parties. These include:
rel="nofollow"for links where the link is not meant to imply approval; these will not be used by search engines when determining the relevance for a page
rel="external"for links to third-party web pages; this can be used as the basis of styling, such as an image that indicates the user will be taken to a separate site
There are a number of techniques that can be used to track which links are followed from a website. Methods that rewrite the links within a web page to point to an interstitial ("you are leaving this website") page or through a script can mislead the user and any automated agents about the target of the link. It is better to use a script to capture
onclick or other events and redirect the user at that point.
In conclusion, publishing on the Web is different from print publishing. This document has enumerated some of these differences, especially those relevant to licencing and copyright issues.
Many thanks to Rigo Wenning and Wendy Seltzer for their reviews and comments on earlier versions of this draft, and to Robin Berjon for ReSpec.js.