Syntax documentation

What does this MR do?

Closes #254 (closed).
Adds a stub for #243.

Changes to public APIs

Author's checklist (required)

• Intermediate commits compile (use git rebase -i main if not)
• Newly added code has a style consistent with the rest of the repository
• Newly added code is documented (guidelines)
• If bugs have been solved, tests have been added (guidelines)

Related issues