I think you are misinterpreting the intent of the documentation: when it refers to 'ZERO_LENGTH' in the equivalence it is talking about actual zero length (ie matching an empty string) rather than potential zero length, such as matching /c?/.

The implication is therefore that, for example:

  /( (?: c? )* )/x

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is treated as equivalent to:
  /( (?: c* | ) )/x

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to break the loop.

Similarly for a more complex zero-length expression such as a lookahead:

  /( (?: a | (?=c) ) )*/x

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is treated as equivalent to:
  /( (?: a* | (?=c) ) )/x

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Hope this helps,

Hugo

In reply to Re: ZERO_LENGTH match by hv
in thread ZERO_LENGTH match by sh1tn

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