Quite often I receive a notification of a chat message, even though I thought I had left the chat room.
If I haven't logged in for a few hours, then this chat message is not in the main 'page' of the chat room.
I would like to respond to most messages, so how can I respond to an older message in chat?
Ref: Add the ability to reply to a chat message directly from the transcript on Meta Stack Overflow.
On the transcript page (where the notification link takes you), open the message menu (by clicking the downward arrow that appears to the left of the message when you hover over it) and click "reply to this message":
(your menu will have slightly less content)
This will take you inside the chat room, with the input box pre-populated for the reply, so you can just start typing your response.
