Moped acces in cycleways - tagging convention

Based on a question raised by Jakka in chat:

For tags regarding access, we use classes ‘A’, ‘B’ and ‘P’ (speedelecs) in the national legislation.
When using tags to show what modes of transport can and cannot access the way, we use thinkgs like:
‘oneway:moped_A = no’ to show that while it’s a one-way for cars, moped_A can use it in both directions.

The question however boils down to the spelling of the tag:
moped_a, moped_b, moped_s versus moped_A’, ‘moped_B’ and 'moped_C.

Jakka himself was leaning towards the lower case version, as he claims to have read once that capital letters in tagging are to be restricted to names. I myself however couldn’t come up with an official source to back up that claim.
They are listed with capital letters on this page:

Ideally, we create a suitable convention and wiki-document it through here: ? (to have it on a more clearly retrievable location?)

I’m however opening up the question from chat to forum (and most likely to the talk-be mailing) for input.

As lionel_giard mention in this list there ar no capital letters in key or value

Indeed. However, there’s not a single case where there’s a letter-based-subcategory added either.
While it shows no evidence pro using capital letters, it also has no clear restriction of counter-examples to say we shouldn’t.

I found two single-letter thingies that’d normally be uppercase:
bdouble=*, to indicate access for B-doubles (a type of road train).
aerialway=t-bar, despite the fact the T is supposed to resemble the lift’s design.

More examples of initialism in keys: url=, iata=, icao=, atv=, 4wd_only=, hgv=, lhv=, psv=, mtb:scale=, sac_scale= (SAC is short for Swiss Alpine Club).
And in values: amenity=bbq, amenity=atm, office=it, office=ngo, shop=atv, sport=bmx, sport=rc_car, route=mtb

I saw no counterexamples. For once, OSM seems to be consistent. I’m in favour of the lowercase variants moped_{a,b,p}.