code: function checkShash(i) {
    const start = i;
    let l;
  
    if (i >= tokensLength) return 0;
  
    if (tokens[i].type === TokenType.NumberSign) i++;
    else return 0;
  
    if (l = checkIdentOrInterpolation(i) || checkPartialIdent(i)) i += l;
    else return 0;
  
    while (i < tokensLength) {
      if (l = checkIdentOrInterpolation(i) || checkPartialIdent(i)) i += l;
      else break;
    }
  
    tokens[start].shashEnd = i;
  
    return i - start;
  }
docs: Check if token is part of a hexadecimal number (e.g. `#fff`) inside a simple
  selector
  @param {number} i Token's index number
  @return {number}