LuaTeX is an extended version of pdfTeX using Lua as an
embedded scripting language. The LuaTeX project's main
objective is to provide an open and configurable variant of TeX
while at the same time offering downward compatibility. LuaTeX
uses Unicode (as UTF-8) as its default input encoding, and is
able to use modern (OpenType) fonts (for both text and
mathematics). It should be noted that LuaTeX is still under
development; its specification has been declared stable, but
absolute stability may not in practice be assumed.
