While there are plug-ins that do this, it should be a function of FileMaker.
1. There is a need to create forms which just cannot be done in Form View or Table View or List View (or in portal), as they may include graphics (such as a test), or need to slide (variable question and/or answer length & height). This can be created and shown in Web Viewer. But submitting that form may not be able to send to a website (which would need to have a database to collect the data).
2. Java script can 'collect' the GET information (name/value pairs) into a single web form field, but getting that data back is not possible with
(which reads the original form, not the completed form).