What are these things?

[OnionTaco22]

I keep seeing these every so often when building maps but I have no idea what they are.

They also don't seem to show up consistently, which also confuses me.

[jaeden]

Those things are for setting vertex heights - you can create a sloped floor/ceiling by moving them up and down.

They only work for (and show for) triangular sectors.

Edited April 13 by jaeden

[Artinum]

If they annoy you, Alt-V should toggle them on and off.

[Stabbey]

That seems very useful. I made a UDMF map which had a city street and sidewalk, with a slope connecting the driveway to the street. Somehow I managed to make a sloped sector which perfectly connected the sidewalk with the driveway ramp without knowing about that feature, but knowing about this seems like I should be able to understand how to do that consistently.