Documentation for porting to other engines/languages

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I am planning on creating my own game engine with compatibility in mind, & I'd like to use quake .map files to empathize compatibility for letting fans create their own levels. I understand godot exists & is decent but like i said I'd like to make my own game engine instead of being forced to work with recent graphic APIs that will restrict what can run my games, not that a steam deck starts at $399 USD.