4. XHTML Abstract Modules

This section is normative.

This section specifies the contents of the XHTML abstract modules. These modules are abstract definitions of collections of elements, attributes, and their content models. These abstract modules can be mapped onto any appropriate specification mechanism. The XHTML 1.1 Specification, for example, maps these modules onto DTDs as described in [XML].

Content developers and device designers should view this section as a guide to the definition of the functionality provided by the various XHTML-defined modules. When developing documents or defining a profile for a class of documents, content developers can determine which of these modules are essential for conveying their message. When designing clients, device designers should develop their device profiles by choosing from among the abstract modules defined here.

4.1. Common Characteristics of Modules

Many of the abstract modules in this section describe elements, attributes on those elements, and minimal content models for those elements or element sets. This section identifies some shorthand expressions that are used throughout the abstract module definitions. These expressions should in no way be considered normative or mandatory. They are an editorial convenience for this document. When used in the remainder of this section, it is the expansion of the term that is normative, not the term itself.

4.1.1. Syntactic Conventions

The abstract modules are not defined in a formal grammar. However, the definitions do adhere to the following syntactic conventions (as defined in Building XHTML Modules [BUILDING]). These conventions are similar to those of XML DTDs, and should be familiar to XML DTD authors. Each discrete syntactic element can be combined with others to make more complex expressions that conform to the algebra defined here.

element name

When an element is included in a content model, its explicit name will be listed.

Content set

Some modules define lists of explicit element names called content sets. When a content set is included in a content model, its name will be listed.

expr ?

Zero or one instances of expr are permitted.

expr +

One or more instances or expr are required.

expr *

Zero or more instances of expr are permitted.

a , b

Expression a is required, followed by expression b.

a | b

Either expression a or expression b is required.

a - b

Expression a is permitted, omitting elements in expression b.

parentheses

When an expression is contained within parentheses, evaluation of any subexpressions within the parentheses take place before evaluation of expressions outside of the parentheses (starting at the deepest level of nesting first).

extending pre-defined elements

In some instances, a module adds attributes to an element. In these instances, the element name is followed by an ampersand (&).

Defining the type of attribute values

When a module defines the type of an attribute value, it does so by listing the type in parentheses after the attribute name.

Defining the legal values of attributes

When a module defines the legal values for an attribute, it does so by listing the explicit legal values (enclosed in quotation marks), separated by vertical bars |, inside of parentheses following the attribute name.

4.1.2. Content Types

The abstract module definitions in this document define minimal, atomic content models for each module. These minimal content models reference the elements in the module itself. They may also reference elements in other modules upon which the abstract module depends. Finally, the content model in many cases requires that text be permitted as content to one or more elements. In these cases, the symbol used for text is PCDATA. This is a term, defined in the XML 1.0 Recommendation, that refers to processed character data. A content type can also be defined as EMPTY, meaning the element has no content in its minimal content model.

4.1.3. Attribute Types

In some instances, the types of attribute values or the explicit set of permitted values for attributes are defined. The following attribute types (defined in the XML 1.0 Recommendation) are used in the definitions of the Abstract Modules:

Attribute Type	Definition
CDATA	Character data
ID	A document-unique identifier
IDREF	A reference to a document-unique identifier
IDREFS	A space-separated list of references to document-unique identifiers
NAME	A name with the same character constraints as ID above
NMTOKEN	A name composed of CDATA characters but no whitespace
NMTOKENS	Multiple names composed of CDATA characters separated by whitespace
PCDATA	Processed character data

In addition to these pre-defined data types, XHTML Modularization defines the following data types and their semantics (as appropriate):

Data types	Description
Character	A single character from [ISO10646].
Charset	A character encoding, as per [RFC2045].
Charsets	A space separated list of character encodings, as per [RFC2045].
Color	The attribute value type "Color" refers to color definitions as specified in [SRGB]. A color value may either be a hexadecimal number (prefixed by a hash mark) or one of the following sixteen color names. The color names are case-insensitive. Color names and sRGB values Black = "#000000" Green = "#008000" Silver = "#C0C0C0" Lime = "#00FF00" Gray = "#808080" Olive = "#808000" White = "#FFFFFF" Yellow = "#FFFF00" Maroon = "#800000" Navy = "#000080" Red = "#FF0000" Blue = "#0000FF" Purple = "#800080" Teal = "#008080" Fuchsia = "#FF00FF" Aqua = "#00FFFF" Thus, the color values "#800080" and "Purple" both refer to the color purple.
ContentType	A media type, as per [RFC2045].
ContentTypes	A comma-separated list of media types, as per [RFC2045].
Datetime	Date and time information.
LanguageCode	A language code, as per [RFC1766].
Length	The value may be either a Pixels or a percentage of the available horizontal or vertical space. Thus, the value "50%" means half of the available space.
LinkTypes	Authors may use the following recognized link types, listed here with their conventional interpretations. A LinkTypes value refers to a space-separated list of link types. White space characters are not permitted within link types. These link types are case-insensitive, i.e., "Alternate" has the same meaning as "alternate". User agents, search engines, etc. may interpret these link types in a variety of ways. For example, user agents may provide access to linked documents through a navigation bar. Alternate Designates substitute versions for the document in which the link occurs. When used together with the xml:lang attribute, it implies a translated version of the document. When used together with the media attribute, it implies a version designed for a different medium (or media). Stylesheet Refers to an external style sheet. See the Style Module for details. This is used together with the link type "Alternate" for user-selectable alternate style sheets. Start Refers to the first document in a collection of documents. This link type tells search engines which document is considered by the author to be the starting point of the collection. Next Refers to the next document in a linear sequence of documents. User agents may choose to preload the "next" document, to reduce the perceived load time. Prev Refers to the previous document in an ordered series of documents. Some user agents also support the synonym "Previous". Contents Refers to a document serving as a table of contents. Some user agents also support the synonym ToC (from "Table of Contents"). Index Refers to a document providing an index for the current document. Glossary Refers to a document providing a glossary of terms that pertain to the current document. Copyright Refers to a copyright statement for the current document. Chapter Refers to a document serving as a chapter in a collection of documents. Section Refers to a document serving as a section in a collection of documents. Subsection Refers to a document serving as a subsection in a collection of documents. Appendix Refers to a document serving as an appendix in a collection of documents. Help Refers to a document offering help (more information, links to other sources information, etc.) Bookmark Refers to a bookmark. A bookmark is a link to a key entry point within an extended document. The title attribute may be used, for example, to label the bookmark. Note that several bookmarks may be defined in each document.
MediaDesc	The MediaDesc attribute is a comma separated list of media descriptors. The following is a list of recognized media descriptors: screen Intended for non-paged computer screens. tty Intended for media using a fixed-pitch character grid, such as teletypes, terminals, or portable devices with limited display capabilities. tv Intended for television-type devices (low resolution, color, limited scrollability). projection Intended for projectors. handheld Intended for handheld devices (small screen, monochrome, bitmapped graphics, limited bandwidth). print Intended for paged, opaque material and for documents viewed on screen in print preview mode. braille Intended for braille tactile feedback devices. aural Intended for speech synthesizers. all Suitable for all devices. Future versions of XHTML may introduce new values and may allow parameterized values. To facilitate the introduction of these extensions, conforming user agents must be able to parse the media attribute value as follows: The value is a comma-separated list of entries. For example, media="screen, 3d-glasses, print and resolution > 90dpi" is mapped to: "screen" "3d-glasses" "print and resolution > 90dpi" Each entry is truncated just before the first character that isn't a US ASCII letter [a-zA-Z] (ISO 10646 hex 41-5a, 61-7a), digit [0-9] (hex 30-39), or hyphen (hex 2d). In the example, this gives: "screen" "3d-glasses" "print" A case-sensitive match is then made with the set of media types defined above. User agents may ignore entries that don't match. In the example we are left with screen and print. Note. Style sheets may include media-dependent variations within them (e.g., the CSS @media construct). In such cases it may be appropriate to use "media =all".
MultiLength	The value may be a Length or a relative length. A relative length has the form "i*", where "i" is an integer. When allotting space among elements competing for that space, user agents allot pixel and percentage lengths first, then divide up remaining available space among relative lengths. Each relative length receives a portion of the available space that is proportional to the integer preceding the "*". The value "*" is equivalent to "1*". Thus, if 60 pixels of space are available after the user agent allots pixel and percentage space, and the competing relative lengths are 1*, 2*, and 3*, the 1* will be alloted 10 pixels, the 2* will be alloted 20 pixels, and the 3* will be alloted 30 pixels.
Number	One or more digits
Pixels	The value is an integer that represents the number of pixels of the canvas (screen, paper). Thus, the value "50" means fifty pixels. For normative information about the definition of a pixel, please consult [CSS1]
Script	Script data can be the content of the "script" element and the value of intrinsic event attributes. User agents must not evaluate script data as HTML markup but instead must pass it on as data to a script engine. The case-sensitivity of script data depends on the scripting language. Please note that script data that is element content may not contain character references, but script data that is the value of an attribute may contain them.
Text	Arbitrary textual data, likely meant to be human-readable.
URI	A Uniform Resource Identifier, as per [URI].
URI	A space separated list of Uniform Resource Identifiers, as per [URI].

4.1.4. Attribute Collections

The following basic attribute sets are used on many elements. In each case where they are used, their use is identified via their name rather than enumerating the list.

Collection Name	Attributes in Collection
Core	class (NMTOKEN), id (ID), title (CDATA)
I18N	dir ("rtl" | "ltr"), xml:lang (NMTOKEN)
Events	onclick (Script), ondblclick (Script), onmousedown (Script), onmouseup (Script), onmouseover (Script), onmousemove (Script), onmouseout (Script), onkeypress (Script), onkeydown (Script), onkeyup (Script)
Style	style (CDATA)
Common	Core + Events + I18N + Style

Note that the Events collection is only defined when the Intrinsic Events abstract module is selected. Otherwise, the Events collection is empty.

Also note that the Style collection is only defined when the Stylesheet Module is selected. Otherwise, the Style collection is empty.

4.2. Basic Modules

The basic modules are modules that are required to be present in any XHTML Family Conforming Document Type.

4.2.1. Structure Module

The Structure Module defines the major structural elements for XHTML. These elements effectively act as the basis for the content model of many XHTML family document types. The elements and attributes included in this module are:

This module is the basic structural definition for XHTML content. The html element acts as the root element for all XHTML Family Document Types.

4.2.2. Basic Text Module

This module defines all of the basic text container elements, attributes, and their content model:

The minimal content model for this module defines some content sets:

Heading

h1 | h2 | h3 | h4 | h5 | h6

Block

address | blockquote | div | p | pre

Inline

abbr | acronym | br | cite | code | dfn | em | kbd | q | samp | span | strong | var

Flow

Heading | Block | Inline

4.2.3. Hypertext Module

The Hypertext Module provides the element that is used to define hypertext links to other resources. This module supports the following element and attributes:

This module adds the a element to the Inline content set of the Basic Text Module.

4.2.4. List Module

As its name suggests, the List Module provides list-oriented elements. Specifically, the List Module supports the following elements and attributes:

This module also defines the content set List with the minimal content model (dl | ol | ul)+ and adds this set to the Flow content set of the Basic Text Module.

4.3. Applet Module

The Applet Module provides elements for referencing external applications. Specifically, the Applet Module supports the following elements and attributes:

When the Applet Module is used, it adds the applet element to the Inline content set of the Basic Text Module.

4.4. Text Extension Modules

This section defines a variety of additional textual markup modules.

4.4.1. Presentation Module

This module defines elements, attributes, and a minimal content model for simple presentation-related markup:

When this module is used, the hr element is added to the Block content set of the Basic Text Module. In additional, the b, big, i, small, sub, sup, and tt elements are added to the Inline content set of the Basic Text Module.

4.4.2. Edit Module

This module defines elements and attributes for use in editing-related markup:

When this module is used, the del and ins elements are added to the Inline content set of the Basic Text Module.

4.4.3. BDO Module

The BDO module defines an element that can be used to declare the bi-directional rules for the element's content.

When this module is used, the bdo element are added to the Inline content set of the Basic Text Module.

4.5. Forms Modules

4.5.1. Basic Forms Module

The Basic Forms Module provides the forms features found in HTML 3.2. Specifically, the Basic Forms Module supports the following elements, attributes, and minimal content model:

This module defines two content sets:

Form

form

Formctrl

input | select | textarea

When this module is used, it adds the Form content set to the Block content set and it adds the Formctrl content set to the Inline content set as these are defined in the Basic Text Module.

4.5.2. Forms Module

The Forms Module provides all of the forms features found in HTML 4.0. Specifically, the Forms Module supports:

This module defines two content sets:

Form

form | fieldset

Formctrl

input | select | textarea | label | button

When this module is used, it adds the Form content set to the Block content set and it adds the Formctrl content set to the Inline content set as these are defined in the Basic Text Module.

The Forms Module is a superset of the Basic Forms Module. These modules may not be used together in a single document type.

4.6. Table Modules

4.6.1. Basic Tables Module

The Basic Tables Module provides table-related elements, but only in a limited form. Specifically, the Basic Tables Module supports:

When this module is used, it adds the table element to the Block content set as defined in the Basic Text Module.

4.6.2. Tables Module

As its name suggests, the Tables Module provides table-related elements that are better able to be accessed by non-visual user agents. Specifically, the Tables Module supports the following elements, attributes, and content model:

When this module is used, it adds the table element to the Block content set of the Basic Text Module.

4.7. Image Module

The Image Module provides basic image embedding, and may be used in some implementations independently of client side image maps. The Image Module supports the following element and attributes:

When this module is used, it adds the img element to the Inline content set of the Basic Text Module.

4.8. Client-side Image Map Module

The Client-side Image Map Module provides elements for client side image maps. It requires that the Image Module (or another module that supports the img element) be included. The Client-side Image Map Module supports the following elements:

When this module is used, the table element is added to the Block content set of the Basic Text Module.

4.9. Server-side Image Map Module

The Server-side Image Map Module provides support for image-selection and transmission of selection coordinates. It requires that the Image Module (or another module that supports the img element) be included. The Server-side Image Map Module supports the following attributes:

4.10. Object Module

The Object Module provides elements for general-purpose object inclusion. Specifically, the Object Module supports:

When this module is used, it adds the object element to the Inline content set of the Basic Text Module.

4.11. Frames Module

As its name suggests, the Frames Module provides frame-related elements. Specifically, the Frames Module supports:

4.12. Iframe Module

The Iframe Module defines an element that can be used to define a base URL against which relative URIs in the document will be resolved. The element and attribute included in this module are:

When this module is used, the iframe element is added to the Block content set as defined by the Basic Text Module.

4.13. Intrinsic Events

Intrinsic events are attributes that are used in conjunction with elements that can have specific actions occur when certain events are performed by the user. The attributes indicated in the following table are added to the attribute set for their respective elements ONLY when the modules defining those elements are selected. Note also that selection of this module defines the attribute collection Events as described above. Attributes defined by this module are:

4.14. Metainformation Module

The Metainformation Module defines an element that describes information within the declarative portion of a document (in XHTML within the head element). This module includes the following element:

4.15. Scripting Module

The Scripting Module defines elements that are used to contain information pertaining to executable scripts or the lack of support for executable scripts. Elements and attributes included in this module are:

When this module is used, it adds the script and noscript elements are added to the Block content set of the Basic Text Module.

4.16. Stylesheet Module

The Stylesheet Module enables style sheet processing. Note also that selection of this module defines the attribute collection Style as described above. The element and attributes defined by this module are:

When this module is used, it adds the style element to the Block content set of the Basic Text Module.

4.17. Link Module

The Link Module defines an element that can be used to define links to external resources. These resources are often used to augment the user agent's ability to process the associated XHTML document. The element and attributes included in this module are:

When this module is used, it adds the link element to the content model of the head element as defined in the Structure Module.

4.18. Base Module

The Base Module defines an element that can be used to define a base URL against which relative URIs in the document will be resolved. The element and attribute included in this module are:

When this module is used, it adds the base element to the content model of the head element of the Structure Module.

4.19. Legacy Module

The Legacy Module defines elements and attributes that were deprecated in previous versions of HTML and XHTML. While the use of these elements and attributes is no longer encouraged, they are provided in this module to ease their integration should markup language authors wish to support them.

When this module is used, it adds the base element to the content model of the head element of the Structure Module.