Please allow me to disagree, at least on definition...
Quote from
http://www.w3.org/TR/REC-xml/
---
The ampersand character (&) and the left angle bracket (<)
MUST NOT
appear
in their literal form, except when used as markup delimiters, or
within a
comment, a
processing
instruction, or a
CDATA section.
If they are needed elsewhere, they
MUST be
escaped
using either
numeric character
references
or the strings "
& " and "
<
"
respectively. The right angle bracket (>)
may be represented
using the string "
> ",
and
MUST,
for compatibility,
be escaped
using either "
> " or a character reference when
it
appears in the string "
]]> " in content, when
that string is not marking the end of a
CDATA
section.