code: function checkClass(i) {
    const start = i;
    let l;
  
    if (i >= tokensLength) return 0;
  
    if (tokens[i].class_l) return tokens[i].class_l;
  
    // Skip `.`.
    if (tokens[i].type === TokenType.FullStop) i++;
    else return 0;
  
    if (l = checkIdentOrInterpolation(i)) i += l;
    else return 0;
  
    while (i < tokensLength) {
      if (l = checkIdentOrInterpolation(i)) {
        tokens[start].class_l = l + 1;
        i += l;
      } else break;
    }
  
    tokens[start].classEnd = i;
  
    return i - start;
  }
docs: Checks if token is part of a class selector (e.g. `.abc`).
  
  @param {number} i Token's index number
  @return {number} Length of the class selector