How to flip texture on a brush face?

[Dreikblack]

For example flip by Y axis to make it match with opposite side of object like door

Texture editing is not an option (using from Quake pak)

[Josh]

Set the texture scale to a negative number.

[andrekyler]

When would you typically need to use the "flip texture" function on a brush face?

[Josh]

If you want to reverse the texture for some reason, like if the text in your image was backwards or you just want to line something up with the scene geometry.