[...] Perl accepts m'^a$q' which can never match... unless /m is somehow implied [...]
With or without the /
m modifier, it can never match against any string whatsoever because as the regex is defined,
$ is required to match before something other than an end-of-string or newline:
'q' follows it in the regex.
If the regex is defined with a newline to follow the $ metacharacter, if the /m modifier is used and if the interpolation-suppressing ' (single-quote) character is used as the regex delimiter, then a match is possible against a string with an embedded newline:
>perl -wMstrict -le
"my $s = qq{a\nq};
print $s =~ m'^a$q' ? ' ' : 'NO ', 'match';
print $s =~ m'^a$q'm ? ' ' : 'NO ', 'match';
print $s =~ m'^a$\nq' ? ' ' : 'NO ', 'match';
print $s =~ m/^a$\nq/m ? ' ' : 'NO ', 'match';
print $s =~ m'^a$\nq'm ? ' ' : 'NO ', 'match';
"
NO match
NO match
NO match
NO match
match
