For example, in this mode, a connection could be established to read a chunk of data, the data could then be modified by the application as required.
In order to actually have the file data submitted, the form must have the requires you specify, the controller action, controller, any additional route parameters, and the form method, before you can finally specify an anonymous object of html attributes where you'll add the is a bit of a magic method.
What it actually does is inspect the type the property specified in the expression and attempt to find a matching editor template for that type.
I have another post that explains editor and display templates in depth, if you're interested.
The basic idea, though, is that these templates tell Razor what HTML it should generate for a property of the type the template implements. Razor has some "default" templates that are used for some types.