#appinfo is a built-in, read-only
stream that provides the value of the
parameter of an SGML declaration.
#appinfo shelf has a value depends on the state of SGML parsing. It has a value only if
the SGML declaration has already been parsed and it had an
appinfo declaration other than
none. If this is not the case, it is unattached. Therefore,
never attached in
do sgml-parseblock, prior to the execution of the first
suppress, unless a pre-compiled DTD is used,
document-endrule, when errors occurred before this information could be determined.
If an SGML declaration was not given, or if
appinfo none was specified in the SGML
#appinfo is unattached.