public boolean matchSequentiallyOptionally(PsiElement el1, PsiElement el2) {
    return (el1 == null && isLeftLooseMatching()) ||
           (el2 == null && isRightLooseMatching()) ||
           matchSequentially(new FilteringNodeIterator(SiblingNodeIterator.create(el1), getNodeFilter()),
                             new FilteringNodeIterator(SiblingNodeIterator.create(el2), getNodeFilter()));
  }
public boolean matchSequentiallyOptionally(PsiElement el1, PsiElement el2)