Runtime instance extensions of profiles

[fosdev]

Allows a service to dictate extension to a profile via:

1. Header convention
2. Well-known

Less not have to fork ALPS. Prevent profile explosion.

What is the best way to do this?

[fosdev]

Overlaps with #5 w/r to what it means to dereferencing processing.

[fosrias]

@mamund I remember us discussing this walking in front of Pier 1 on the embarcadero 😛 .

I think is actually part of a broader topic around externally extending existing profiles, e.g. something like an overlay ALPS def. I don't see another topic on this.

So will drop a thought or two here. I think we want to point an extension at a descriptor or maybe an ALPS doc, right?

If I have a "profile" header, I could have to ALPS docs there IIUC. One of them could be the unmodified ALPS doc followed by a link to the "overlay" or whatever doc. This is still tricky cause the extension doc wants to extend another profile. We could do something like this:

<alps extends="http://some_profile>
  <ext id="some_extension" extends="#descriptor ref cause it treats it as local"/>
</alps>

Actually, thinking about it, I would not need the other profile. This would say, deref the extended profile and add these changes.

Thoughts?