On Thu, 14 Jan 2016, Alexander Dyomin wrote:

> Dear list,
> when I stumble upon a slightly overhanging line (where it's not allowed to hyphenate the hanging word and putting it on next line leaves huge whitespaces), decreasing letterspacing in that line seems like a good idea, and I manually insert \kerncharacters commands to do the trick. Here's a MWE for the purpose of demonstration:
>
> % ConTeXt code
> \setuppapersize[A5]
> \setupbackgrounds[text] [rightframe=on,framecolor=red,rulethickness=0.1pt] %right margin line
>
> \setupalign[hz,hanging] % microtypography enabled
> \definefontfeature[default][default][protrusion=quality,expansion=quality]
>
> \definetypeface[mainface][rm][specserif][Linux Libertine O] [default]
> \setupbodyfont[mainface,14pt]
>
> \mainlanguage[russian]
> \setupindenting[yes,medium,first]
>
> \starttext
>
> {\kerncharacters[-0.018] Здесь будет длинный-предлинный текст, \mbox{в~коем}} никак нельзя перенести строку. 
> Запрещено { \kerncharacters[-0.008] разрывать телефонные номера, например, \mbox{(000)1234-5678}}, многозначные числа и дефисные написания.
> \stoptext
>
>
> Is the a way for automating such negative tracking?

I seem to remember seeing a demo (either by Hans or Idris) for Arabic 
typesetting where some optimizations were performed after the linebreaks. 
I wonder if similar approach could be used here.

Aditya