Description of problem:
I'm trying to install an application with the necessary config to ensure that
this application will be opened whenever files of a certain type is
double-clicked under the GNOME desktop.

Unfortunately, how this is done is *completely undocumented* as far as I can
tell. Also, the config that has worked in the past no longer does, i.e.
mentioning the MIME type in /usr/share/application-registry/<name>.applications.
And what I thought may be the new way of doing it, i.e. including

MimeType=<my type>

in /usr/share/applications/<name>.desktop does not seem to help, either.
 

I trying really hard not to star yelling, now. This constant changing of how
things work *without providing compatibility for old-style config* must change
right now. Also, as far as I can tell, no config mechanism has been standardised
by freedesktop.org. Why change from something that works reasonably well to
something else that's nonstandard, when a new standard is right around the corner?

Version-Release number of selected component (if applicable):
2.8.1-4

How reproducible:
Every time

Steps to Reproduce:
You know what I mean