Is it really possible to add new keywords into QScintilla lexer?

I am wondering if we can add new keywords(custom keywords) into QScintilla lexer. I know there are different lexer types available in QScintilla but my file contains cpp and some assembly codes. So I wanted to add some keywords in existing cpp lexer. It is mentioned that by making subclass of lexer class we should be able to add keywords using below function

But somehow I am not able to successfully add my keywords into already specified ones.
Could you please guide me to achieve this? Any hint or suggestion will be highly appreciable.