4.6 Predefined Entities
Predefined Entities
Entity and character references MAY
both be used to escape the left angle bracket, ampersand, and
other delimiters. A set of general entities (amp,
lt,
gt,
apos,
quot) is specified for
this purpose. Numeric character references MAY also be used; they are expanded
immediately when recognized and MUST be treated as character data, so the
numeric character references "<" and "&" MAY be used to escape < and & when they occur
in character data.
All XML processors MUST recognize these entities whether they are declared
or not. For interoperability, valid XML
documents SHOULD declare these entities, like any others, before using them. If
the entities lt or amp are declared, they MUST be
declared as internal entities whose replacement text is a character reference
to the respective
character (less-than sign or ampersand) being escaped; the double
escaping is REQUIRED for these entities so that references to them produce
a well-formed result. If the entities gt, apos,
or quot are declared, they MUST be declared as internal entities
whose replacement text is the single character being escaped (or a character
reference to that character; the double escaping here is OPTIONAL but harmless).
For example:
<!ENTITY lt "&#60;">
<!ENTITY gt ">">
<!ENTITY amp "&#38;">
<!ENTITY apos "'">
<!ENTITY quot """>
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