I find it clumsy that multi-word directive names in device and font description files use '_' instead of '-' to separate words.  Perhaps this is because I don't subscribe to the sermon preached by many C language programmers that everything in the world should look like C.

This would pleasantly pave the way for some modest reforms like 'thin-space-width' and 'hair-space-width' (see comment #6 of bug #55154) and synonymous alternate spellings of existing directives.  Consider 'paper-format', 'size-scale', 'has-t-command', 'unit-width' (maybe this one should have a more distinct and communicative synonym, like 'design-size' [but see grodvi(1) :-/ ]), and 'space-width'.