4.1. Common Attributes

The following attributes occur in several of the elements and are defined here for brevity. In general, all attribute names and values in this specification are case insensitive, except where noted otherwise. The ID, CLASS and attributes are required for use with style sheets, while LANG and DIR are needed for internationalization.

   <!ENTITY % attrs
          "id      ID       #IMPLIED  -- element identifier --
           class   NAMES    #IMPLIED  -- for subclassing elements --
           lang    NAME     #IMPLIED  -- as per RFC 1766 --
           dir   (ltr|rtl)  #IMPLIED  -- I18N text direction --">

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. It allows authors to distinguish different roles played by the same tag. The classes may be used by style sheets to provide different renderings as appropriate to these roles.

LANG

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.

DIR

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.

When applied to TABLE, it indicates the geometric layout of rows (i.e. row 1 is on right if DIR=RTL, but on the left if DIR=LTR) and it indicates a default base directionality for any text in the table's content if no other DIR attribute applies to that text.