>>>> I am currently working on some galley-related code, and looking at the
>>>> e-TeX extensions to Knuth's paragraph-breaking penalty system. The roles
>>>> of \clubpenalties, \widowpenalties and \displaywidowpenalties are clear,
>>>> and it seems reasonable to provide a documented interface to these
>>>> primitives. On the other hand, \interlinepenalties

Context uses it in \keeplinestogether, but I don't see why they
couldn't have used \clubpenalties instead. I don't understand the
difference between \interlinepenalties and \clubpenalties as described
in etex_man:

- the ith interline penalty value is used after line i of the paragraph;
- the ith club penalty value is used after line i of a partial paragraph;

All other hits on Google are either irrelevant, l3names, context, or
on the german ctt (perhaps some info there).

--
Bruno