HTML and Style Sheets 23 Jan 96 INTERNET DRAFT Bos, Raggett & Lie, Expires in six months World Wide Web Consortium HTML and Style Sheets Status of this Memo This document is an Internet draft. Internet drafts are working documents of the Internet Engineering Task Force (IETF), its areas and its working groups. Note that other groups may also distribute working information as Internet drafts. Internet Drafts are draft documents valid for a maximum of six months and can be updated, replaced or obsoleted by other documents at any time. It is inappropriate to use Internet drafts as reference material or to cite them as other than as "work in progress". To learn the current status of any Internet draft please check the "lid-abstracts.txt" listing contained in the Internet drafts shadow directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East coast) or ftp.isi.edu (US West coast). Further information about the IETF can be found at URL: http://www.ietf.org/ Distribution of this document is unlimited. Please send comments to the HTML working group (HTML-WG) of the Internet Engineering Task Force (IETF) at . Discussions of this group are archived at URL: http://www.acl.lanl.gov/HTML-WG/archives.html. This specification is also available via the Web in hypertext form as a Working Draft of the World Wide Web Consortium, see: http://www.w3.org/pub/WWW/TR Authors: Bert Bos , Dave Raggett , Hakon Lie ------------------------------------------------------------------------------ Abstract 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 Bos, Raggett & Lie Page 1 HTML and Style Sheets 23 Jan 96 does not specify particular style sheet notations, leaving that to other specifications. Contents * Associating HTML documents with style sheets ...................... 2 * Media dependencies ................................................ 3 * The LINK element .................................................. 3 * The STYLE element ................................................. 4 * Common attributes ................................................. 5 * The SPAN element .................................................. 7 * The DIV element ................................................... 7 * User interface and user supplied style sheets * Performance issues ................................................ 9 * Limitations of this specification ................................. 9 * References ....................................................... 10 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. Bos, Raggett & Lie Page 2 HTML and Style Sheets 23 Jan 96 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: ACME Widgets Corp

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If your browser supports style sheets, try our new look in old, new and wacky styles. ... This specification builds upon the definition of the LINK element in HTML 2.0 (RFC 1866) in the following respects: Bos, Raggett & Lie Page 3 HTML and Style Sheets 23 Jan 96 * The forward link type "stylesheet" is hereby defined to signify that the associated LINK element specifies a link to a style sheet that may be applied to the HTML document containing the LINK element. The HREF attribute specifies the network address of the linked style sheet. * If there are several such links, then these are considered as providing a choice of alternative style sheets. The character string supplied with the TITLE attribute is recommended for use in building a menu of alternative styles. Note that the order of such LINK elements in the document markup does not signify preference order. * The TYPE attribute may be used to specify the Internet Media type and associated parameters for the linked style sheet. This allows the user agent to disregard style sheets in unsupported notations, without the need to first make a remote query across the network. 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. Title The STYLE element is formally defined by: The attributes are defined as follows: Bos, Raggett & Lie Page 4 HTML and Style Sheets 23 Jan 96 TYPE 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. TITLE 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. Some characters may require escaping with their SGML entity names: "&" followed by a letter or "#" character should be represented by "&" while "<" followed by a letter, "!" or "?" character should be represented by "<". 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. The rendering implied by the STYLE element is independent of such LINK elements, i.e. it is not cascaded with style sheets specified by 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. Bos, Raggett & Lie Page 5 HTML and Style Sheets 23 Jan 96 ID 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. CLASS 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. STYLE A text string providing rendering information specific to this element. The notation is specified with the STYLE element in the document head. For example: Test Document

The first few words of this article is in small-caps. This would be formatted to look something like: THE FIRST few words of this article is in 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 the HTML EM element is allowed. The DIV element Bos, Raggett & Lie Page 7 HTML and Style Sheets 23 Jan 96 The DIV element is used with the CLASS attribute to represent different kinds of containers, e.g. chapter, section, abstract, or appendix. DIV allows the enclosed group of elements to be given a distinctive style. For example:

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The DIV element can be used anywhere that the HTML P element is allowed. The content model for DIV allows headers, lists, paragraphs as well as other DIV elements etc. This allows DIVs to be nested, to form hierarchies of chapters, sections, and subsections etc. DIV can be used with an ALIGN attribute to specify the default horizontal alignment for the contents of the DIV element. This is needed for compatibility with deployed browsers and may be overriden by style sheets. ALIGN=LEFT Lines are aligned flush left ALIGN=CENTER Lines are centered. ALIGN=RIGHT Lines are aligned flush right ALIGN=JUSTIFY Lines are justified where practical, otherwise this has the same effect as ALIGN=LEFT 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 Bos, Raggett & Lie Page 8 HTML and Style Sheets 23 Jan 96 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. "styletype", 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 itself, e.g. in CSS one can specify: Title Bos, Raggett & Lie Page 9 HTML and Style Sheets 23 Jan 96 References 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. CSS "Cascading style sheets" by Hakon 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 ------------------------------------------------------------------------------ The World Wide Web Consortium: http://www.w3.org/ Bos, Raggett & Lie Page 10