I am running into the problem with requestValidationMode="4.0"
where if you submit html tags in a form the request will be marked as invalid and the app will throw A potentially dangerous Request.Form value was detected from the client
.
The two most popular solutions are to use requestValidationMode="2.0"
combined with validateRequest='false'
on either a global level or keeping global as 4.0
but making a subdirectory that is listed as 2.0
in its web.config and putting all the pages that you don't want validated there.
What I would really like is to keep 4.0 but add a little logic to the 4.0 RequestValidator class to prevent it from throwing an error if it's just HTML in a form.