[NTG-context] fit to width by negative letterspacing or narrowing

Hello again, it's been a while... ;-) I need to pack fixed lines into a fixed width box. Some years ago I had something similar in plain PostScript, where I pre-calculated the width of a text box, let the default font if it would fit my max size, otherwise try a narrow font and if that wasn’t enough decreased font size until it would fit. This time I've only one font and must not decrease font size, but must use negative kerning and perhaps some artificial narrowing. How can I do that with ConTeXt? I use MkIV, so any Lua solution is welcome. Greetlings from Lake Constance! Hraban --- http://www.fiee.net/texnique/ http://wiki.contextgarden.net https://www.cacert.org (I'm an assurer)