pseudocode
----------

$aXML =~ s@`@<backtick>@gs;

while ( commands remain unprocessed )
   {
    foreach match for <any_command>
       {
        substitute for <`any_command>
        set found_command boolean flag true
       }

    if (found_command)
      {
       while ( find match for <`command>data</command> ) 
            {
             process if (
                         no nested ` chars found             
                        )

            }
      }
   }