Dave, if you've ever written a function that begins with the characters "m", "q", "s", "tr", or "y", you'd understand why moo parses as 'moo' and not m//... ;)

Honestly, though, I doubt you will find the use of alpanumberscores as delimiters documented. The closest I came was erroneous documentation in perlop:

The lack of processing of \\ creates specific restrictions on the post-processed text. If the delimiter is /, one cannot get the combination \/ into the result of this step. / will finish the regular expression, \/ will be stripped to / on the previous step, and \\/ will be left as is. Because / is equivalent to \/ inside a regular expression, this does not matter unless the delimiter happens to be character special to the RE engine, such as in s*foo*bar*, m[foo], or ?foo?; or an alphanumeric char, as in:

  m m ^ a \s* b mmx;
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In the RE above, which is intentionally obfuscated for illustration, the delimiter is m, the modifier is mx, and after backslash-removal the RE is the same as for m/ ^ a s* b /mx). There's more than one reason you're encouraged to restrict your delimiters to non-alphanumeric, non-whitespace choices.

The documentation is plain wrong, as far as what it's telling you, but shows the use of "m" as the delimiter.

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Jeff[japhy]Pinyan: Perl, regex, and perl hacker.
s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;