A slate to write and draw on, then export to html

new test

For commit ff88a2a927 which fixed a regression caused by commit e51ce12969.

I'm trying to provide enough guardrails for myself and future readers without causing a combinatorial explosion in tests. The previous commit was able to get more value out of existing tests, but this test feels necessary. And useful in general without reference to a specific bug.

Created by  Kartik K. Agaram  on June 12, 2022
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