Section 9.5, "Character Reference" says that a numeric character
reference should be treated just like the character it references. But
if the number isn't in the domain of the document character set, what
character does the reference refer to? I'd say this is a reportable
markup error.
My reading of the following text from ISO 8879 would indicate otherwise:
13.1.2 Non-SGML Character Identification
Each character number to which no meaning is assigned by the
character set description is assigned to NONSGML, thereby
identifying it as a non-SGML character.
^^^^^^^^^^^^^^^^^^^^
4.267 reportable markup error : A failure of a document to
conform to this International Standard when it is parsed with
respect to the active document and link types, other than a
semantic error ... or : ^^^^^^^^^^
...
f) the occurrence of a non-SGML character
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Glenn