<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def tokens(self):
 """Further breaks down all tokens for a particular expression into words and other expressions. ['var x = 10'] """

        for content in self.contents:
            if isinstance(content, TokenWithPosition):
                for word in content.split():
                    yield word
            else:
                yield content