When I go to http://mm-ch.wmflabs.org/wiki/Special:CreateMassMessageList and select the "Import pages from an existing list or category" radio button to activate the "Source" text field input, if I enter an invalid input (e.g. the non-existent page "fsdfdsfsdffffff"), I'm only warned post-form submission.

We can use AJAX to warn the user prior to form submission. This would be a better user experience.

Version: unspecified
Severity: enhancement
Whiteboard: gci2014