[Dev-luatex] string library with utf-8 support

Hello, I developped a Japanese dictionnary in XeTeX. It compiles just fine in luatex but I would like to code the commands in Lua instead of TeX. To make the code faster, cleaner, simpler and more powerfull. Yet, I need to be able to manipulate utf-8 strings (find, substring, replace, length, etc...). Is there a simple way to do that in LUA ? Will there be one day a luatex library for utf8 string managments ? (because it seems the string library is just for strings with 1 byte characters and it is really lacking) Keep up the good work. Olivier Binda