It looks like something has changed in the options when using the _Line command. In V8 if you wanted your line Perpendicular to a curve you hit ‘P’, in V9 this has changed, the ‘r’ is underscored instead. Doesn’t make sense to change from what did make sense 
Yeah, that looks like a bug. The V8 FourPoint option previously had F as a shortcut which left P available for Perpendicular, in the WIP FourPoint has been renamed to 4Point (no idea why) and since shortcuts must be letters and not numbers, the P got taken over by that…
the reason is explained here: RH-79314 Line: FourPoint option is renamed 4Point
if its by design fair enough, I still don’t get it
Underlined letters have never been very consistent across commands, since they get assigned based on the first available character. So in Sphere, 4Point is not p but i.
This would need a more general debate about how that is handled I think.
Well in this case the ‘reason’ may make it match semantically, but does not work practically, plus the change also risks to invalidate macros. So personally I think it’s shooting yourself in the foot.
This has happend in the past with other commands. IIRC the attribution of the one letter aliases to command line options is an automatic function that arttributes the letters on a first-come-first-served basis from left to right - but that can be overridden by special casing on a command-by-command basis. So either change the order of options so that Perpendicular comes before 4Point so P is automatically assigned to it, or override it as a special case. In that case 4Point would probably end up being o.
We already had this case with Revolve in V6 (?) and earlier where the FullCircle option was u because F was already taken by something else. IIRC, the position of the option was just moved to the left to force the F. I don’t have V5 or V6 installed on this computer so I can’t check, but I’m virtually certain this was the case.
yes, in case someone has a macro _Line p instead of _Line Perpendicular, that would screw up the macro.
I would also prefer having the p for perpendicular.
RH-94757 _Line option Perpendicular is r instead of p
sometimes the old cliche of-‘if it ain’t broke, don’t fix it’ should be considered 
thanks 