code: function atrequire() {
      var pos = position();
      var m = match(new RegExp('^@require *([^;\\n]+);'));
      if (!m) return;
  
      var val = trim(m[1]);
      m = new RegExp('^"([^"]+)" +as +([a-zA-Z_][a-zA-Z0-9_]*)$').exec(val);
      if (!m) return;
  
      return pos({
        type: 'require',
        id: trim(m[2]),
        require: trim(m[1])
      });
    }
docs: Parse require