Not really familiar with how all the RB extensions work, but this looks pretty good otherwise. I only have a few minor nitpicks and questions (see opened issues).

Should go alphabetical: pygments.formatters then pygments.lexers

Any potential for IOError (e.g. file doesn't exist)?  This might be handled elsewhere, so feel free to ignore if this is the case.

Two spaces between the imports and functions, one space between the functions.

Also, not sure if there's any precedent (or desire to go this way), but Django's class-based generic views would let you add these views inline in your urls.py modules. E.g. in urls.py, the url would look like:

url(r'^$', TemplateView.as_view(template_name="xml_review_ui_extension/configure.html")

along with the appropriate import. See https://docs.djangoproject.com/en/1.4/topics/class-based-views/ for more on class-based views. The project mentors may not be into using them, so if you're interested, double-check before going down that road.

I think this will all fit in one line

This should go right after "import logging"

Add a blank line between these two lines

Add space between these two lines

This looks cool, but just like the markdown change, we'll need some form of commenting.

What configuration are you planning on adding?

Because 1.7 requires Python 2.5 and newer, we can now use the "with" structure here to make this nicer.

Indentation looks off here.

I think it will read a little easier if you put "extension" on the next line. Also indent only 4 spaces from the "super"

Add two blank lines above each function.

This looks a bit long for one line. Try moving the "% PACKAGE" To the next.

Two blank lines.

I don't think we need to subclass everything. What I'd prefer is to just instantiate a URLHook and pass it the patterns. Keeps things simpler.

Same comment.

Same.

Should inherit from FileAttachmentReviewable.

Those defaults are available in that parent class. The only one you introduce is 'rendered', which should be the only entry in here.

I don't really know why we have this. I'd say unless there's an immediate reason for some dashboard, remove it.

This is looking pretty good. My major comments are about the naming of the files, which doesn't match our conventions.

This file should be called xml_review_ui.py

Is this line too long?

This file should be mimetypes.py

This file should be xmlReviewableView.js

So this looks good, but it's not the right repository for it. Any extensions should go in rb-extension-pack. I'm moving it to there and committing!