Can we get a discussion going on the desirability of the "F4 support" patches that Robbbbbert is submitting? I vote "wastes memory and execution time and clutters the drivers for no useful reason", but MESS has never had adult supervision before so I assume they will continue to go in.
In case it's not clear: F4 is a developer aid, not a user feature. It not working for a driver is not considered a problem. Since the drivers the support is being added to all already can decode and display the characters properly there is no developer benefit to them either.
While I agree, MESS needs more overall quality control you have to look at things in context.
I looked over some of the changes, and they have no performance hit. This is case #1, they're a one time decode, which decode the character stored in the BIOS rom.
Case #2 is dynamic decodes (which decode characters as they're uploaded to RAM) *do* have a cost, especially if they're not needed by the driver, which obviously if they're added as an afterthought aren't.
Of course in case #1 you'll only ever get the same decode every time you run the driver. The characters never change, they're the bios characters, they're not very interesting*
In case #2, the characters will change. If you're developing a driver, this might be useful to indicate how far a specific game has gone towards loading, has it ever uploaded gfx data, or did it get stuck before that point? It can be considered a useful dev aid, if the developers of that driver need it.
As with MAME, there are 2 groups of users. Developers using the code, to make improvements, and end-users, just using it to play games. Benefits to the first group can be very important, benefits to the 2nd group, a little less-so. You could argue that having F4 available (on dynamic drivers) benefits the developers (seeing what's uploaded) but puts players at a disdavantage (slower speed).
For changes like this that's what is important, you need to weigh up the cost / benefit, in some cases they're useless, in other cases not so much. The ones checked in so far are harmless, but ultimately not very interesting. They add no value, but they have no cost aside a few lines of easily understandable code.
* For console / computer systems where they'll likely only contain the BIOS font, obviously MAME is different where most of the game GFX are usually in static ROM.