The Selection Source dropdown is unlocked when you select an item or employee Section Type.
You can incorporate your employee and/or material list into your custom forms. By selecting the "Item Selection" or "Employee Selection" Section Type, it will automatically pull your material or employee list into the Selection Source field. This allows the field user to select names or materials from a dropdown menu on the mobile app.
The Selection Source is either locked/greyed out, or is auto-populates based on the Section Type selection, it cannot be altered manually.