Numeric character reference: Difference between revisions

Revision as of 06:59, 18 July 2004

Revision as of 12:24, 20 September 2004

Line 41:

While the syntax of SGML does not prohibit unassigned code points such as  from being referenced, SGML-derived markup languages such as HTML and XML can, and often do, restrict numeric character references to reference only those code points that have not been assigned to characters (rather, code points not permanently unassigned).

Restrictions may also apply for other reasons. For example, in HTML 4, , which is a reference to a non-printing "form feed" control character, is allowed (because a form feed character is allowed), but in XML, the form feed character cannot be used, not even by reference. As another example, €, which is a reference to another control character, cannot be used or referenced in HTML, but it is allowed in HTML. Furthermore, XML 1.0, being based on an older version of ISO 10646, prohibited using characters above U+FFFD except in character data, thus making a reference like 𐀁 illegal, while in XML 1.1, such a reference is allowed, because the available character repertoire was explicitly extended.