The file `init.lua` in pandoc's data directory is run as part of
pandoc's Lua initialization process. Previously, the `pandoc` module was
loaded in `init.lua`, and the structure for marshaling was set-up after.
This allowed simple patching of element marshaling, but made using
`init.lua` more difficult:
- it encouraged mixing essential initialization with user-defined
customization;
- upstream changes to init.lua had to be merged manually;
- accidentally breaking marshaling by removing required modules was
possible;
Instead, all required modules are now loaded before calling `init.lua`.
The file can be used entirely for user customization. Patching
marshaling functions, while discouraged, is still possible via the
`debug` module.
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