CharacterData and represents the
content of a comment, i.e., all the characters between the starting
'<!--' and ending '-->'. Note that this is
the definition of a comment in XML, and, in practice, HTML, although some
HTML tools may implement the full SGML comment structure.
No lexical check is done on the content of a comment and it is
therefore possible to have the character sequence "--"
(double-hyphen) in the content, which is illegal in a comment per section
2.5 of [XML 1.0]. The
presence of this character sequence must generate a fatal error during
serialization.
See also the Document Object Model (DOM) Level 3 Core Specification.