There are a couple of addons out there which create a "/clear" command to erase all the text in a chat window. Those have the disadvantage (IMHO) that they also erase all the scrollback text. Personally, I want to clear all the currently displayed text, but be able to view it again if I want to. So I wrote this addon. "Clearing" the window only forces all the text to instantly fade out, as if you had waited a few mintues.

"/clear" clears all chat windows.
"/clear N" clears chat window number N.
"/clear print" prints each chat window's number to that chat window, so you have a reference.
"/clear <any other text>" print out a help statement like this one.

Huge credit goes to Maldivia of Sargeras realm, who gave me the trick behind how SetTimeVisible and SetFadeDuration interact in 1.9 and older, and to Iriel of the UI forums, who pointed out the cycle trick that needed to be made for 1.10.