[NTG-context] \installlanguage syntax

Hi, I'm student at Faculty of Informatics at Masaryk university and I'm writing bachelor's thesis this year. One part of the thesis is to document language support and implementation in ConTeXt so someone can use it to implement new language. Right now I'm stuck with command \installlannguage. I can't figure out what these parametres are doing: \c!leftsentence=---, \c!rightsentence=---, \c!leftsubsentence=---, \c!rightsubsentence=---, So I'would really appreciated some more info about them. Thank you for your answers. Tomas Pustelnik