W3C: WD-style-960118

HTML3 and Style Sheets

W3C Working Draft 18-Jan-1996

This version:
Latest version:
Bert Bos <bert@w3.org>,
Dave Raggett <dsr@w3.org>,
Håkon Lie <howcome@w3.org>

Status of this document

This is a W3C Working Draft for review by W3C members and other interested parties. It is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to use W3C Working Drafts as reference material or to cite them as other than "work in progress". A list of current W3C working drafts can be found at: http://www.w3.org/pub/WWW/TR

Note: since working drafts are subject to frequent change, you are advised to reference the above URL, rather than the URLs for working drafts themselves.


The HyperText Markup Language (HTML) is a simple markup language used to create hypertext documents that are portable from one platform to another. HTML documents are SGML documents with generic semantics that are appropriate for representing information from a wide range of applications. This specification extends HTML to provide support for style rules expressed in separately specified notations. It is no longer necessary to extend HTML when new styles are needed. Style rules can be (a) included with individual HTML elements to which they apply, (b) grouped together in the document head, or (c) placed in associated style sheets. This specification does not specify particular style sheet notations, leaving that to other specifications.


Associating HTML documents with Style Sheets

There are several approaches for associating HTML documents with separate style sheets:

User applied style sheets
The user agent may provide the means for users to select and apply style sheets.

Implicit associations
The appropriate style sheet may be implied by the URL or other information describing the resource. This approach allows style sheets to be retrieved in advance of, or at the same time as, the HTML document itself. Implicit associations are not defined in this report.

Explicit associations
The author can specify one or more alternative style sheets for an HTML document using one of the methods described below.

In HTML it is also possible to put style sheets in-line in the document. HTML is extended with a new element and a new attribute (both called STYLE), as described below. No matter how style is associated with HTML, the user should be made aware that a particular style has been applied and should have the option of turning it off.

To make it easier to apply a style to parts of a document, two new elements for use in the body of an HTML document are defined: DIV and SPAN. The first is to enclose a division (chapter, section, etc.) of a document, making it possible to give a whole section a distinctive style. The latter is used within paragraphs, similarly to EM, but in cases where none of the other HTML elements (EM, STRONG, VAR, CODE, etc.) apply.

Media dependencies

Styles may often be designed for a restricted range of media, e.g. for graphical user interfaces with scalable fonts and millions of colors; for A4 paper media; for speech output; or for simple terminals with one monospace font. This proposal doesn't provide an explicit means to state the conditions under which a given style sheet is applicable.

Style sheet notations may themselves provide support for media dependencies. Another approach is to use a generic URL to reference a style sheet, and to make the binding to a specific URL according to the media required. This will be described in a separate working draft.

The LINK element

In HTML, the LINK element is used to create a typed hyperlink between the document and some other resource. The REL attribute defines the type of the link. With REL=stylesheet, the LINK element can also be used to link to a style sheet.

Authors can use LINK elements to offer readers a choice of style sheets, e.g:

    <LINK TITLE="Old" REL=stylesheet HREF="old.style" TYPE="application/dsssl">
    <LINK TITLE="New" REL=stylesheet HREF="new.style" TYPE="application/rtf">
    <LINK TITLE="Wacky" REL=stylesheet HREF="wacky.style" TYPE="text/css">
    <TITLE>ACME Widgets Corp</TITLE>

    <H1>ACME Widgets Corp</H1>
    <P>If your browser supports style sheets, try our new look
    in traditional, modern and wacky styles.

Another approach is to use a generic URL for a LINK which maps to a set of alternative style sheets. A separate working draft will describe how resource descriptions can be used for this purpose.

This specification builds upon the definition of the LINK element in HTML 2.0 in the following respects:

        href    CDATA     #REQUIRED  -- Universal Resource Locator --
        title   CDATA     #IMPLIED   -- advisory title string --
        rel     CDATA     #IMPLIED   -- forward link type --
        rev     CDATA     #IMPLIED   -- reverse link type --
        type    CDATA     #IMPLIED   -- Internet media type --

The STYLE element

A single STYLE element may be included in the document head. It allows authors to include style rules within the HTML document, e.g.

    <STYLE TYPE="text/css">
      H1 { color: brown }
      P  { color: blue  }

The STYLE element is formally defined by:

    <!ELEMENT style - O (#PCDATA)>
    <!ATTLIST style
        type     CDATA    #REQUIRED -- Internet media type for style --
        title    CDATA    #IMPLIED  -- advisory title for this style --

The attributes are defined as follows:

This required attribute defines the style notation as an Internet Media type including associated parameters. It is used in the same way as with LINK elements. The type applies to style rules in the STYLE element as well as those attached with the STYLE attribute.

The user agent is recommended to use the title string when building a menu of alternative style sheets. This will only happen if the STYLE element occurs together with linked style sheets as specified by one or more LINK elements. In the absence of such LINK elements, the TITLE attribute may be used to describe the style sheet for the purpose of allowing the user to turn style sheets on and off.

The content model for the STYLE element precludes SGML tags, and the end tag of a STYLE element can usually be omitted, e.g. when the STYLE element is followed by another element. Instances of the characters "&", "<" or ">" within style rules should be escaped using SGML entities, e.g. &amp; &lt; and &gt; respectively.

When the STYLE element occurs together with one or more LINK elements that specify linked style sheets, the user agent should consider the STYLE element in preference to the LINK elements.

Common attributes

To support effective use of style sheets with HTML documents a number of common attributes are proposed. These can be used with most HTML elements. In general, all attribute names and values in this specification are case insensitive, except where noted otherwise.

<!ENTITY % attrs
       "id      ID       #IMPLIED  -- element identifier --
        class   NAMES    #IMPLIED  -- for subclassing elements --
        style   CDATA    #IMPLIED  -- rendering annotation --
        lang    NAME     #IMPLIED  -- as per RFC 1766 --
        dir   (ltr|rtl)  #IMPLIED  -- I18N text direction --">
Used to define a document-wide identifier. This can be used for naming positions within documents as the destination of a hypertext link. It may also be used by style sheets for rendering an element in a unique style. An ID attribute value is an SGML NAME token. NAME tokens are formed by an initial letter followed by letters, digits, "-" and "." characters. The letters are restricted to A-Z and a-z.
A space separated list of SGML NAME tokens. CLASS names specify that the element belongs to the corresponding named classes. These may be used by style sheets to provide class dependent renderings.
A text string providing rendering information specific to this element. The notation is specified with the STYLE element in the document head.

For example:

    <TITLE>Test Document</TITLE>
    <STYLE TYPE="text/css">
    <P STYLE="color: red; font-style: small-caps">This text should
     be in small capitals and colored red!

The end tag for the STYLE element has been omitted here since the element is unambiguously ended by the <P> start tag.

A LANG attribute identifies the natural language used by the content of the associated element.The syntax and registry of language values are defined by RFC 1766. In summary the language is given as a primary tag followed by zero or more subtags, separated by "-". White space is not allowed and all tags are case insensitive. The name space of tags is administered by IANA. The two letter primary tag is an ISO 639 language abbreviation, while the initial subtag is a two letter ISO 3166 country code. Example values for LANG include:
      en, en-US, en-uk, i-cherokee, x-pig-latin.
Human writing systems are grouped into scripts, which determine amongst other things, the direction the characters are written. Elements of the Latin script are nominally left to right, while those of the Arabic script are nominally right to left. These characters have what is called strong directionality. Other characters can be directionally neutral (spaces) or weak (punctuation).

The DIR attribute specifies an encapsulation boundary which governs the interpretation of neutral and weakly directional characters. It does not override the directionality of strongly directional characters. The DIR attribute value is one of LTR for left to right, or RTL for right to left, e.g. DIR=RTL.

The SPAN element

    <!ELEMENT span O O (%text)*>
    <ATTLIST c
            %attrs;     -- id, class, style, lang and dir --

Sometimes it is desirable to apply a style to some text which doesn't have a structural role or established rendering convention. For instance, the first few words of an article may be rendered as small capital letters ("small-caps"). In such situations it is inappropriate to use an existing tag such as EM: on existing user agents the first few words would be mysteriously italicized. The new SPAN tag is recommended instead, as it has no effect on existing user agents.

An example based on CSS:

    <STYLE TYPE="text/css">
    SPAN { font-style: small-caps }
    <P><SPAN>The first</SPAN> few words of this article is small-caps.

This would be formatted to look something like:

    THE FIRST few words of this 
    article is small-caps.

While on an existing user agent it would look like:

    The first few words of this 
    article is small-caps.

The SPAN element can be used anywhere that EM is allowed. In the HTML DTD, the %phrase entity is modified thus:


The DIV element

    <!ELEMENT div - - (%body.content)*>
    <ATTLIST c
            %attrs;     -- id, class, style, lang and dir --

HTML lacks an element that can group paragraphs, headers, etc. into a chapter, a section, an abstract, etc. The DIV element is added to deal with this situation. It can enclose elements so that they can be given a distinctive style as a group.

DIVs can be nested, to form, e.g., a hierarchy of chapters, sections, and subsections. The %body.content entity in the HTML DTD must be modified:

    <!ENTITY % body.content "(DIV|%heading|%block|HR|ADDRESS|IMG)*">

(recommended) or:

    <!ENTITY % body.content "(DIV|%heading|%text|%block|HR|ADDRESS)*">

User interface and user supplied style sheets

In an interactive user agent, the user should be made aware that a particular style sheet has been applied, and be given the option of turning it off or selecting a different style. A flag in the corner of the window and a toggle in a menubar can be sufficient.

It may be possible for the user to combine several of the available style sheets. It should be possible for the user to choose a personal style instead of, or in combination with, style sheets supplied by the author.

When a user agent applies a style sheet to a document while the author of that document has indicated a preference for a different style sheet, the user agent may have to alert the user to that fact. Exactly how and when that is done is outside the scope of this report. E.g., the CSS style sheet language gives rules for the conditions under which a user is allowed to override the author's choices.

Performance issues

Some people have voiced concerns over performance issues for style sheets. For instance, fetching a LINKed style sheet may delay the full presentation for the user. A similar situation arises if the document head includes a lengthy set of style rules.

The current proposal sidesteps these issues by allowing authors to include rendering instructions within each HTML element. The rendering information is then always available by the time the user agent wants to render each element.

In many cases, authors will take advantage of a common style sheet for a group of documents. In this case, distributing style rules throughout the document will actually lead to worse performance than using a linked style sheet, since for most documents, the style sheet will already be present in the local cache. The public availability of good style sheets will encourage this effect.

Limitations of this specification

This specification limits the number of STYLE elements to one per document. If later revisions allow multiple STYLE elements in the document head (e.g. to cater for alternative styles) one will need a different way of specifying the style notation for STYLE attributes on the elements in the document body. The suggested choice is an attribute on the BODY element, e.g. "stylenotation", with the same definition as the "type" attribute for the STYLE element.

Also, there is no way to specify that two or more style sheet are to be merged. A common case is where the style of a document is based on an organization-wide style sheet (which is likely to be cached), but needs document-specific overrides. This functionality may be added in the future, but can also be provided by the style sheet notation. E.g., in CSS one can specify:

    <STYLE TYPE="text/css">
      @import "house-style.css"
      @import "draft-report.css"
      H1 { color: red }     /* override cascaded style sheets */


RFC 1866
"Hypertext Markup Language - 2.0" by T. Berners-Lee & D. Connolly, November 1995. This document can be downloaded from ftp://ds.internic.net/rfc/rfc1866.txt.
RFC 1766
"Tags for the Identification of Languages", by H. Alvestrand, UNINETT, March 1995. This document can be downloaded from ftp://ds.internic.net/rfc/rfc1766.txt.
"Cascading style sheets" by Håkon Lie & Bert Bos, December 1995. The latest version of this document can be downloaded from http://www.w3.org/pub/WWW/TR/WD-css1.html

W3C: The World Wide Web Consortium: http://www.w3.org/