code: function position() {
      var start = { line: lineno, column: column };
      if (!options.position) return positionNoop;
  
      return function(node){
        node.position = {
          start: start,
          end: { line: lineno, column: column },
          source: options.source
        };
  
        whitespace();
        return node;
      }
    }
docs: Mark position and patch `node.position`.