League\CommonMark\Cursor::advanceBySpaceOrTab PHP Method

    public function advanceBySpaceOrTab()
    {
        $character = $this->getCharacter();
        if ($character === ' ' || $character === "\t") {
            $this->advanceBy(1, true);
            return true;
        }
        return false;
    }

 public function matchesNextLine(Cursor $cursor)
 {
     if (!$cursor->isIndented() && $cursor->getFirstNonSpaceCharacter() === '>') {
         $cursor->advanceToFirstNonSpace();
         $cursor->advance();
         $cursor->advanceBySpaceOrTab();
         return true;
     }
     return false;
 }