8.3.5 Forbidden Patterns
M4sugar provides a means to define suspicious patterns, patterns
describing tokens which should not be found in the output. For
instance, if an Autoconf configure script includes tokens such as
‘AC_DEFINE’, or ‘dnl’, then most probably something went
wrong (typically a macro was not evaluated because of overquotation).
M4sugar forbids all the tokens matching ‘^m4_’ and ‘^dnl$’.
— Macro: m4_pattern_forbid
Declare that no token matching pattern must be found in the output.
Comments are not checked; this can be a problem if, for instance, you
have some macro left unexpanded after an ‘#include’. No consensus
is currently found in the Autoconf community, as some people consider it
should be valid to name macros in comments (which doesn't make sense to
the author of this documentation, as ‘#’-comments should document
the output, not the input, documented by ‘dnl’ comments).
Of course, you might encounter exceptions to these generic rules, for
instance you might have to refer to ‘$m4_flags’.
— Macro: m4_pattern_allow
Any token matching pattern is allowed, including if it matches an