The list of hot keys at the end of Training Mission IV says that the "z" key will max/min the chat window. The big list of keys says that "z" is for "select enemy in front". There's nothing listed for "min/max chat window", but F2 seems to do that.

A minor thing, but I thought I'd pass it on.

z "does" maximize the chat, but only on a PDA screen.

Hot keys are not the same as control keys, as you cannot re-bind them, and are not listed on the F1 screen.