sub match {
  shift =~ m/
       (?:    [^(]*\((?<C>[^)]*?)\)    )    # Both parens.
    |  (?:    \((?<C>.*)$              )    # Left paren.
    |  (?:    ^(?<C>.*)\)              )    # Right paren.
    |  (?:    ^[^()]*(?<C>)$           )    # No parens (empty capture).
  /x;
  return $+{C} // ();
}