code: function checkClass(i) {
    let l;
  
    if (i >= tokensLength) return 0;
  
    if (tokens[i].class_l) return tokens[i].class_l;
  
    if (tokens[i++].type === TokenType.FullStop) {
      if (l = checkInterpolatedVariable(i)) tokens[i].class_child = 1;
      else if (l = checkIdent(i)) tokens[i].class_child = 2;
      else return 0;
  
      tokens[i].class_l = l + 1;
      return l + 1;
    }
  
    return 0;
  }
docs: Check if token is part of a class selector (e.g. `.abc`)
  @param {Number} i Token's index number
  @returns {Number} Length of the class selector