In the modeler you can set the 'allowed extensions'
but this will not filter the files you actually see in the file select dialog, and you can still select all file types.
But when the allowed extension is, for example, 'pdf' I only want to be able to select pdf's.
This is very easy to achieve by adding the 'accept' attribute to the <input> tag.
This is now possible by using the SetAttribute widget, but Mendix really should support this by default..