Other fields

Some examples of other key: names one could use.

url: http://fossil.example.org/wiki/plugin
Usually just used for the main script, as project homepage link.
api-docs: http://doc.example.org/
link to manual
src: http://stackoverflow.com/questions/*
Code origin reference
Menu / Icons
icon: fire.png
Could be relative file reference, or some application-level fixed icons/ dir.
base64 embedded icon (as used in streamtuner2)
img: Either embedded or file reference / just an alias
hidden: e.g. hide plugin entry from main menu
keycode: Alt+F4
Keycombinations for GUI apps
key: cp│copy
Regex aliases for CLI interfaces
Plugin management
sort: -100
Ordering for plugin loading, if they're instantiated on startup but some are pre-dependencies.
priority: core
How essentional is this plugin (core, default, optional, contrib, obsolete). Can be utiized for grouping plugins in admin UI.
support: none
Indicate if plugin is actively supported, or unmainted contrib/

Coincidentally, the format syntax overlaps and jives well with other e.g. Python tool use:

Tooling overlap
format: black formatter option
pylint: flags
classifiers: trove
console-scripts: setup.py/flit wrapper
suggests: softer dependencies
pack: fpm/xpm relative file references/renames/target
architecture: fpm/xpm