function containerOf(a, b) {
  while (b = b.parent) {
    if (a === b) return true;
  }
  return false;
}
function containerOf(a, b) {
  while (b = b.parent) {
    if (a === b) return true;
  }
  return false;
}
function containerOf ( a , b ) { while ( b = b . parent ) { if ( a === b ) return true ; } return false ; }
Checks if container `a` is a container of `b`
Checks if container a is a container of b