code: String[] asStringArray() {
          if (mOrderingStrings == null) {
              String[] orderings = new String[mSize];
              OrderingList<S> node = this;
              for (int i=mSize; --i>=0; ) {
                  orderings[i] = node.mProperty.toString();
                  node = node.mParent;
              }
              mOrderingStrings = orderings;
          }
          return mOrderingStrings;
      }
docs: Returns the orderings as qualified string property names. Each is
  prefixed with a '+' or '-'.
  
  <p>This method is not public because the array is not a clone.