RiscLua is a small, easily learned, programming language
for RISC OS, based on Lua. See the Lua Homepage for information about books on Lua, manuals, mailing lists, etc.
RiscLua for Beginners An Introduction to using RiscLua.
Around PEGs Using the lpeg library.
The sources page has some technical details which may give a clue
to how RiscLua differs from standard Lua.