Symfony\Component\CssSelector\XPathExpr::addStarPrefix PHP Method

    public function addStarPrefix()
    {
        /*
        Adds a /* prefix if there is no prefix.  This is when you need
        to keep context's constrained to a single parent.
        */
        if ($this->path) {
            $this->path .= '*/';
        } else {
            $this->path = '*/';
        }
        $this->starPrefix = true;
    }

 /**
  * undocumented function
  *
  * @param XPathExpr $xpath
  * @param mixed     $expr
  * @param Boolean   $last
  * @param Boolean   $addNameTest
  *
  * @return XPathExpr
  */
 protected function _xpath_nth_child($xpath, $expr, $last = false, $addNameTest = true)
 {
     list($a, $b) = $this->parseSeries($expr);
     if (!$a && !$b && !$last) {
         // a=0 means nothing is returned...
         $xpath->addCondition('false() and position() = 0');
         return $xpath;
     }
     if ($addNameTest) {
         $xpath->addNameTest();
     }
     $xpath->addStarPrefix();
     if ($a == 0) {
         if ($last) {
             $b = sprintf('last() - %s', $b - 1);
         }
         $xpath->addCondition(sprintf('position() = %s', $b));
         return $xpath;
     }
     if ($a < 0) {
         if ($b < 1) {
             $xpath->addCondition('false()');
             return $xpath;
         }
         $sign = '<=';
     } else {
         $sign = '>=';
     }
     $expr = 'position()';
     if ($last) {
         $expr = 'last() - ' . $expr;
         $b--;
     }
     if (0 !== $b) {
         $expr .= ' - ' . $b;
     }
     $conditions = array(sprintf('%s %s 0', $expr, $sign));
     if (1 !== $a && -1 !== $a) {
         $conditions[] = sprintf('(%s) mod %d = 0', $expr, $a);
     }
     $xpath->addCondition(implode(' and ', $conditions));
     return $xpath;
     /* FIXME: handle an+b, odd, even
        an+b means every-a, plus b, e.g., 2n+1 means odd
        0n+b means b
        n+0 means a=1, i.e., all elements
        an means every a elements, i.e., 2n means even
        -n means -1n
        -1n+6 means elements 6 and previous */
 }