AllowChat

AllowChat is one of the oldest grid rules, added in Prerelease 0.0.8a when chat wasn't a thing yet. Controls chat behavior: with rule set to True you will see a normal chat tab and with this rule set to false you will see "THE CHAT IS DISABLED ON THIS GRID" sign. However you still can write text into it and commands will execute normally, but normal text will just disappear after pressing enter. In some early versions there was a bug how to send messages (using /say command) and make chat visible (see commands in next paragraph)

Control commands
/rule AllowChat [true/false]

enabling chat again:

/var game.chat.maxDisplay 20 (Working on lower versions, 20 is a default value)