Improve documentation

I think we can improve the documentation by including a bit more type information, and by including more copy-paste-friendly examples. I've found some of the documentation to gloss over the types of variables, or assume that some variables exist, and it makes the examples hard to understand / reproduce.

The issue names no documentation files, tests, or examples. Start by locating documentation pages and examples that omit variable types or rely on unstated variables, then identify which examples cannot be copied and reproduced as written. Done means the selected documentation explains relevant variable types and uses self-contained, copy-paste-friendly examples.

Written by the indexing model from the issue text.