I have started working on this and will have a pull request submitted by the end of the week. 

The term "whitespace" appears in several contextual situations throughout the documentation. While all situations would benefit from the definition of "whitespace" contained in the str.isspace() documentation, not all of the situations would benefit from a link to str.isspace() whose primary goal is to document the str.isspace() function and not to provide a global definition of what a whitespace character is.

Therefore I suggest the documentation of Python 3 create a new glossary definition of "whitespace" (which contains the definition currently in the str.isspace() documentation) and is pointed to wherever the term "whitespace" is used in any documentation related to strings - including this specific case of strip()/lstrip()/rstrip().