code: private final void checkInvariants() throws Error {
  
          if (_lineBreak == null) {
              throw new Error("_lineBreak == null");
          } else if (_lineBreak == LineBreak.NONE && _indentation.length() > 0) {
              throw new Error("_lineBreak == LineBreak.NONE && _indentation = \"" + _indentation + "\".");
          } else if (_elementStack == null) {
              throw new Error("_elementStack (" + _elementStack + " == null");
          } else if (_elementStackSize < 0) {
              throw new Error("_elementStackSize (" + _elementStackSize + ") < 0");
          }
      }
docs: Checks all invariants. This check should be performed at the end of
  every method that changes the internal state of this object.
  
  @throws Error if the state of this <code>XMLOutputter</code> is invalid.