Actually, it's not an obvious question until you get more familiar with regular expressions. In a nutshell: "don't use them to parse HTML." HTML is simply too complex and arbitrary for a reasonable regex to handle. You need to try something like HTML::Parser instead.

If you go down the mis-guided path of trying to write regexes to parse HTML, eventually, you'll wind up with monstrosities like this:

    $data =~ s/
                (                      # Capture to $1
                  <a\s                 #     <a and a space character
                  (?:                  #     Non-capturing parens
                    [^>](?!href)       #         All non > not followe
+d by href
                  )*                   #         zero or more of them
                  href\s*              #     href followed by zero or 
+more space characters
                ) 
                (                      # Capture to $2
                  &#61;\s*             #     = plus zero or more space
+s
                  (                    #     Capture to $3
                    &[^;]+;            #         some HTML character c
+ode (probably " or ')
                  )?                   #         which might not exist
                  (?:                  #     Non-grouping parens
                    .(?!\3)            #         any character not fol
+lowed by $3
                  )+                   #         one or more of them
                  (?:
                    \3                 #     $3 
                  )?                   #     (which may not exist)
                )
                (                      # Capture to $4
                  [^>]+                #     Everything up to final >
                  >                    #     Final >
                )
            /$1 . decode_entities($2) .  $4/gsexi;
[download]

Which I was trying to debug in this node.

Sorry for the bad news.

Cheers,
Ovid

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