Summary
-------

Given a file with an unknown extension, it is impossible to create an Open With association only for files with that extension: the association is made to all files of the same type, and the unknown extension is ignored. 

For example, a plain text file ``test.program`` will always be treated by Nautilus as text/plain, with no way to tell it that we want to treat *.program files differently from other plain text files. Well, no way short of editing the MIME database by non-Nautilus means. Which is nae user-friendly.


Observed behaviour (setup)
-------------------------------------

Create two text files with unregistered extensions::

    echo "asdf" > test.program     # want to open this with gVim
    echo "aoeu" > test.manuscript  # want to open this with gEdit

(Known extensions are listed in ``/usr/share/mime/globs``.)

Nautilus will recognise both as "text/plain", friendly name "plain text document". 

"Open With" associations can be changed via 

  * right-click > Open With > Other Application... > 
    check "Remember this application for 'plain text document";

  * or, alternatively, via right-click > Properties > Open With > radioboxes. 


Observed behaviour (the bit that should go differently)
-------------------------------------------------------

Changing the "Open With" association of either file will change the association for all files of type "text/plain"; thus, if I 

    1. set test.program to open with gVim, and then 
    2. set test.manuscript to open with gEdit, then 
    3. double-clicking test.program will open it in gEdit, and not in gVim.


Desired behaviour
-----------------

That at step 1 and 2 above, we get to choose whether we we want to make the "Open With" association

    * Just this once, or
    * Remember this for all plain text documents with 
      extension .program (or .manuscript), or
    * Remember this for all plain text documents

This will probably require that Nautilus register the new MIME type, say as "text/x-manuscript", or perhaps "text/x-ext-manuscript" --- I know knothing about the MIME system, myself. Also register "text/x-manuscript" as a subclass of "text/plain".