Much of the new wording here is borrowed from [ChipTheme], [SliderTheme], or [RadioThemeData], which I think are pretty good. I believe a lot of other theme classes have similar wording too. I've also made some tweaks of my own, notably the references to [MaterialApp.theme].

This started from a desire to have clearer cross-references pointing at what to do with a FooThemeData to make it take effect:
  https://github.com/flutter/flutter/pull/135879#discussion_r1355851481
but then as I started writing I kept finding more and more small things I wanted to adjust, including a couple of bits that were extraneous or obsolete.