Familiar with regular come in, 0 wide assertion using repetition * will error resolution

Familiar with the regular coming in, 0 wide assertion using repetition * will error
Everybody look at these two.

PHP Code

  
  Preg_match (' # (? <=a*) word# ', ' pre word ', $MT);p Reg_match (' # (?<=< (\w+) >). * (?=<\/\1>) # ', ' prehi! Word ', $mt);

------Solution--------------------
Http://perldoc.perl.org/perlretut.html#Looking-ahead-and-looking-behind
This is a regular document for Perl and I think it should be available for PHP's regular engine.
Inside there is a sentence of the lookahead assertion is denoted by (? =regexp) and the lookbehind assertion are denoted by (? <=fixed-regexp)
0 Wide assertion is also called surround, which means that the reverse look can only contain a fixed length of sub-expressions, so it cannot appear *? + These quantifiers, only the sequential surround can

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