0 when callout number n is reached for the nth time
  \C*n       pass the number n (may be negative) as callout data; this is used as the callout return value
  \D         use the <b>pcre_dfa_exec()</b> match function
  \F         only shortest match for <b>pcre_dfa_exec()</b>
  \Gdd       call pcre_get_substring() for substring dd after a successful match (number less than 32)
  \Gname     call pcre_get_named_substring() for substring "name" after a successful match (name termin-
               ated by nex