Is 

/
  (
    (?<=prefix)
    (infix)
    (?=suffix)
  )
  (??{ print $^N })
/gx

[download]
really the same as 
/
  prefix
  (infix)
  suffix
  (??{ print $^N })
/gx

[download]
as far as $^N = 'infix' is concerned? Actually I can't seem to find any net differences in the above. I came to this presumption after having used the former for awhile and tested it with a fairly simple RE (such as the above), but wanted to confirm this is universally true for literal strings and ask if it might break otherwise.

Similarly, if they are equivalent, why doesn't 

/
  (
    (?<=some(optional)?prefix)
    (infix)
    (?=suffix)
  )
  (??{ print $^N })
/gx

[download]
optimize away to 
/
  some(optional)?prefix
  (infix)
  suffix
  (??{ print $^N })
/gx

[download]
instead of resulting in the Variable length lookbehind not implemented in regex error?

Lastly, (this might be redundant given answers to the above, but) when is usage of ?<= and ?= appropriate? The only possibility I can think of is something involving nested (), but I can only think of contrived examples at the moment. I seem to recall needing them in the past, but I can't seem to recall the implementation...

In reply to Regular Expression Constructs ?<= and ?= by eibwen

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