I was typing a PM to another user and it was not very succinct, and when I clicked Send the page reloaded, with an error message saying it exceeded 3500 characters, and the message was a garbledygook of HTML/URL form escapes (tons of percent signs).

I.e, it wasn't the original message I typed, and impossible to edit and fix. I tried clicking the Back button on the browser, and of course the message draft was gone.

Requests:
1. Warn the user as they type if they go over, don't wait until they submit the message
2. Block the user from clicking submit until the length issue is corrected

Obviously you'll need a server-side check on this too, not just client side (in case someone gets clever with scripts and tries to submit a yuge message bypassing client side validation).

Click back and copy what you had typed.

Probably too late now though.

Doesn't work on all browsers.