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My "pet" regex I've been playing with for a few days. 
 my $simples = qr{\*\*};  # extensible by user.  Same opening and clos
+ing.
 my $ps= qr{(?<prematch>.*?)
     (?:
       (?<link>
          (?: \[\[\s*(?<body>.*?)\s*\]\]   )  # explicit use of bracke
+ts
          | (?:  (?<body>(?:http|ftp)s?://\S+)   )   # bare (just a st
+art)
       )(*:link)
     | ~ (?<body> (?&link)|.|\Z  ) (*:escape)
     | // \s* (?<body>(?: (?&link)  | . )*?)  \s*  (?: //|\Z)(*:italic
+)  # special rules for //, TODO start no problem, skip any links in b
+ody.
     |  (?<simple>$simples)\s*(?<body>.*?)\s*(?:\k<simple>|\Z)(*:simpl
+e)
     | \\\\ (*:break)
     | \{{3} \s* (?<body>.*?) \s* \}{3} (*:nowiki)  # be sure to check
+ for three braces before checking for two.
     | \{{2} \s* (?<link>[^|]*?) \s* (?:  \|  (?<alt>.*?)  \s* )?   \}
+{2} (*:image)
     | \<{3} \s* (?<body>.*?) \s* \>{3} (*:placeholder)  # be sure to 
+check for 3 angles before checking for 2 (extension)
     | \Z (*:nada)  # must be the last branch
    )
    }xs;

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