Retrieves the position in bytes of the capturing parentheses named
name is a valid sub pattern name but it didn't match anything (e.g. sub pattern "X", matching "b" against "(?P<X>a)?b")
end_pos are set to -1 and true is returned.
name of the subexpression
pointer to location where to store the start position, or null
pointer to location where to store the end position, or null
true if the position was fetched, false otherwise. If the position
cannot be fetched,