PM message content validation (and invalid fields highlighting) with not valid data

Preconditions
You should have registered user and logged it.
You should start test execution from new private message form page.

Example
'a' - Short string. Message should be between 2 and 20000 characters
' a' - Short string. Begin at space.Message should be between 2 and 20000 characters
'a ' - Short string. End at space.Message should be between 2 and 20000 characters
'' - empty string
more than 20000 chars - see attached link.