Sending Text to the Chat Window
 

Is it possible to send custom message to the chat window from another part of the UI. I.E. A bag mod that sends everything to the chat window when it's opened or a button in the bag window is pressed.

All / commands are also available to UI scripting, so you can use /say etc. If you only want to send something to the chat entry line, the command is /beginchatinput.