When using the keyboard to change the volume or brightness, mate displays a big box in the center of the screen by default. It would be nice to be able to disable this. This could be useful for people who don't like distraction, or for people who want to use some alternative (such as ubuntu's notify-osd, or elementary's pantheon-notify).
I believe Ubuntu patched this in a non-customizable way when they introduced notify-osd:
I've made a pull request for this issue (the second one, excuse me please for the deleted first one). But there's the following question: This mentiones a brightness osd, but I can't find one. Does MATE have a brightness osd?
Yes - but it's in https://github.com/mate-desktop/mate-power-manager (it has some code copied from here).