Unicode Explained

—i.e., notations of the form &# n ; or &#x n ;. The document character set is the character

code (mapping of integers to characters) according to which the n in such notations is

to be interpreted.

In particular, HTML and XML specifications do not impose Unicode semantics on

characters, for two reasons: they formally refer to ISO 10646, not the Unicode standard,

and even if they referred to Unicode, this would not constitute a requirement on con-

formance to the standard. Of course, software that processes HTML or XML docu-

ments may apply Unicode semantics and rules, such as line breaking rules, but this is

not a requirement. Only for some features related to directionality do HTML specifi-

cations refer to Unicode rules normatively.

The HTML specifications contain some special restrictions on the use of control char-

acters, as listed in Table 11-2. There is usually little reason why control characters other

than line breaks and sometimes horizontal tabs would appear in HTML documents.

They may, however, appear due to conversions. The rules for them are somewhat dif-

ferent in HTML up to and including HTML 4.01 and in XHTML. (Technically, the

SGML declaration for HTML 4.01 disallows U+000C, but the prose discusses it as an

allowed character. It would anyway be whitespace and not a page eject character.)

Table 11-2. C0 and C1 Control characters in HTML

Character(s) Explanation Use in HTML

U+0000..U+0008 ...