Matt McKay

- [x] testing completed on real world lecture repository https://github.com/QuantEcon/lecture-python.myst/pull/670

`# custom figsize for this lecture`

thanks @HumphreyYang

@HumphreyYang please ping me when you're ready for review.

@HumphreyYang -- nicely written issue!

@choldgraf we discussed this in the context of `solutions` to exercises in `sphinx-exercise` extension. Here is some past discussions on identifying an way forward for this: https://github.com/executablebooks/sphinx-exercise/issues/24 but no `final`...

@latourfranco in https://github.com/executablebooks/sphinx-exercise/pull/45 we are working on a `gated` syntax for directives that would enable `code-cell` to be executed as it remains as the root level of the document. This...