I love the feature of "Editing source code example in the proper mode". It's
very handy and powerful.
I found a bug with org-mtags.el. The table of content tag in muse is
<contents>, but in org is <content>.

If I write a simple org file with the misspelled tag:
----8<----8<---
<contents>
* title1
* title2
----8<----8<---

then export using "C-c C-e h" will lead to a loop
in  org-mtags-get-tag-and-attributes.

I wish I can use <contents> to be consistent with muse, and get a warning
from org if the tag is not supported.