What is Tkinter's tkapp?

I'm using Tkinter in Python, 开发者_Python百科and trying to create code to run when a text box's value is changed. All the code I find online uses a mysterious tk member of Tkinter widgets, and I can't find any documentation on it! I found it's of type tkapp, but there's no documentation on that either.

Where can I find a decent resource which explains to me the workings of this mysterious thing? (Even better, where can I just find documentation on Tkinter? All I can find are tutorials).

Probably the best single resource for Tkinter is this page in the Python.org wiki. There is also the documentation in the Python Library Reference (for 2.7 and for 3.2). Unfortunately, because much of Tkinter is basically a wrapper around existing Tk functionality, a lot of the documentation for Tkinter assumes you know Tk already so reading the Tk documentation is important, too.

tkapp is the highest "master". If you make a widget on the root window, tkapp is the master of that.