Trying to parse non well-formed XML using NSXMLParser

I am parsing XML Data using NSXMLParser and I notice now, that the Elements can contain ALL characters, including for example a &. Since the parser is giving an error when it comes across this character I replaced every Occurence of this character.Now I want to make sure to handle every of these characters that may cause Errors.What are they and how do you think I should handle these characters best? Thanks in advance!