Aha! One of the classic mistakes was made on this code:

 
$myvar =~ /"           # First quote 
            (          # Capture text to $1 
             (?:       # Non-backreferencing parentheses 
               [^?"]   # Anything that's not a question mark or quote 
                |      # or 
               \?[^"]  # A question mark not followed by a quote (to a
+llow embedded question marks) 
             )*        # Zero or more 
            )          # End capture 
          \?"/x;       # Followed by a question mark and quote
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Try this with

$myvar = q{ abc"def??"ghi?"jkl };
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And you'll see that it matches the ghi, not def??. The problem is that the "question mark NOT followed by a quote" can sometimes eat up the question mark that you need to begin your closing delimiter.

The proper way to tackle this is to "inch-along"...

$myvar = q{ abc"def??"ghi?"jkl };

print "matched <$1>" if
$myvar =~ /"           # First quote
            (          # Capture text to $1
             (?:       # Non-backreferencing parentheses
                (?!\?") # not question quote?
                .       # ok to inch along
             )*        # Zero or more
            )          # End capture
          \?"/sx;       # Followed by a question mark and quote
[download]

which properly prints:

matched <def?>
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I was tackling this kind of thing a lot when people would keep posing the "how do I match a C comment?" back in the early days Pre-Ilya-RE. I got pretty good at breaking just about any regex that claimed to match a comment, by undoing any assumption made.

-- Randal L. Schwartz, Perl hacker