[NTG-context] "Trial typesetting" in ConTeXt / lua ?

Dear all, Is it possible in ConTeXt within lua code to do “trial typesetting” (not sure that’s best name for what I would like to achieve) ? By this I mean store some input (with text and macros) in some buffer and do what ConTeXt does normally (parsing, create nodes …) but instead of shipping the nodes to line breaking algorithm and to the page output, only retrieve the nodes and after discard them. This is to get an estimate of the total text width within a paragraph (to calculate some shape on the paragraph). I browsed the lua code from http://source.contextgarden.net/ but I do not dare to use too low level lua functionality. Many thanks for any hint (even a pointer to lua function). Best regards Joseph Canedo