code: function checkSelector1(i) {
    if (i >= tokensLength) return 0;
  
    const start = i;
    let l;
  
    if (l = checkCompoundSelector(i)) i += l;
    else return 0;
  
    while (i < tokensLength) {
      let space = checkSC(i);
      const comma = checkCombinator(i + space);
      if (!space && !comma) break;
  
      if (comma) {
        i += space + comma;
        space = checkSC(i);
      }
  
      if (l = checkCompoundSelector(i + space)) i += space + l;
      else break;
    }
  
    tokens[start].selectorEnd = i;
    return i - start;
  }
docs: Checks for selector which starts with a compound selector.