Here's some information about wall tags and what they do.
Walls tagged [1,0]
Any wall with a Hi-Tag of 1 is excluded from all types of lighting effects (its shade is forced to stay constant).
Walls tagged [0,MirrorSound]
Any wall with the MIRROR (#560) texture overtile (i.e. masked texture) will play MirrorSound when a player presses the action button on the mirror. Effectively, this allows you to make any texture seemingly play a sound effect, simply by hiding a masked and tagged MIRROR texture in front of it.
Walls tagged [ActivationSound,Channel]
Any solid (non-masked) wall with a Switch or DOORTILE texture and a Channel Lo-Tag can trigger an effect when operated. Link the Channel value of the Switch or DOORTILE texture to an Activator (or ActivatorLocked/MasterSwitch). When the player presses the action button on the texture, the Activator (or ActivatorLocked/MasterSwitch) will be triggered. It is also possible to activate the texture by kicking it! This is compatible with any Switch texture, or texture that has the name DOORTILE appended to it. ActivationSound is optional and doesn't apply to Combination Switches. Check the "References - Special Textures" section for the complete texture lists and further details.