def ssml_sub(self, words, alias=None, **kwargs):
return self.nest(SsmlSub(words, alias=alias, **kwargs))<EOL>
Create a <Sub> element

:param words: Words to be substituted
:param alias: Substitute a different word (or pronunciation) for selected text such as an acronym or abbreviation
:param kwargs: additional attributes

:returns: <Sub> element