A texcombiner defines how textures are blend together / what color/alpha values they return. Luxinia comes with a bunch of predefined combiners that the shadercompiler uses and which you can access in the shaderscript. If those are not enough or you need specific operations to be done you can define your own combiners. You must make sure they run well, as there wont be error checking. GL_ARB_texture_env_combine is the main extension this system builds on.
o-+ renderinterface o-+ texcombiner o-- texcombalpha o-- texcombcolor o-- texcombop o-- texcombsrc