code: function $(tok) {
          var match, args, length, index, k;
  
          //
          // Non-terminal
          //
          if (tok instanceof Function) {
              return tok.call(parser.parsers);
          //
          // Terminal
          //
          //     Either match a single character in the input,
          //     or match a regexp in the current chunk (chunk[j]).
          //
          } else if (typeof(tok) === 'string') {
              match = input.charAt(i) === tok ? tok : null;
              length = 1;
              sync ();
          } else {
              sync ();
  
              if (match = tok.exec(chunks[j])) {
                  length = match[0].length;
              } else {
                  return null;
              }
          }
  
          // The match is confirmed, add the match length to `i`,
          // and consume any extra white-space characters (' ' || '\n')
          // which come after that. The reason for this is that LeSS's
          // grammar is mostly white-space insensitive.
          //
          if (match) {
              skipWhitespace(length);
  
              if(typeof(match) === 'string') {
                  return match;
              } else {
                  return match.length === 1 ? match[0] : match;
              }
          }
      }
docs: Parse from a token, regexp or string, and move forward if match