perl -e "'FGTXYZGTFABCGHABC' =~ /[XYZ]{3}([A-Za-z]{0,21})[ABC]{3}/; 
         print $-[0] . ', ' . length($1);"
__OUTPUT__
3, 8

[download]
Note that the output for your first example is 3, 8 instead of 3, 3. The appropiate RegEx for that would have been /[XYZ]{3}([A-Za-z]{0,21}?)[ABC]{3}/ (non-greedy quantifiers).
Hope this helped.

In reply to Re: nested pattern matching by CombatSquirrel
in thread nested pattern matching by vinforget

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