Vis
A vi-like editor based on Plan 9's structural regular expressions
...Efficient syntax highlighting is provided using Parsing Expression Grammars, which can be conveniently expressed using Lua in the form of LPG. The editor core is written in a reasonable amount of clean (your mileage may vary), modern and legacy-free C code, enabling it to run in resource-constrained environments. The implementation should be easy to hack on and encourage experimentation. There is also a Lua API for in-process extensions. Vis strives to be simple and focuses on its core task: efficient text management.