They can be configured to appear when a user uploads a file, usually on the Upload component or Workspace level.
These metaforms function similarly to other metaforms, with a few exceptions. When an upload metaform is presented, the upload will eventually pause, waiting for the metaform to be submitted. Once done, the metadata is added and the files, now MediaBeacon assets, are moved to the designated upload location.
It's common to have one or more fields be required to be filled in order to submit any values on the form. In this state, a field will have a "Required Value" indicator.
No values will be entered and the download will not continue until a value is entered into all required fields. If not, an error will be shown for each field still required.
To cancel an upload at this stage, the user may click the "X" button in the upper right of the Upload dialog.