Often there is more than one way of matching a regular expression at a particular
        location, for POSIX basic and extended regular expressions, the "best"
        match is determined as follows:
      
- 
            Find the leftmost match, if there is only one match possible at this
            location then return it.
          
- 
            Find the longest of the possible matches, along with any ties. If there
            is only one such possible match then return it.
          
- 
            If there are no marked sub-expressions, then all the remaining alternatives
            are indistinguishable; return the first of these found.
          
- 
            Find the match which has matched the first sub-expression in the leftmost
            position, along with any ties. If there is only on such match possible
            then return it.
          
- 
            Find the match which has the longest match for the first sub-expression,
            along with any ties. If there is only one such match then return it.
          
- 
            Repeat steps 4 and 5 for each additional marked sub-expression.
          
- 
            If there is still more than one possible match remaining, then they are
            indistinguishable; return the first one found.