Laura Wienpahl

No one was assigned to do this by the feature freeze for v3.5.0, so we postpone to v3.6 (or later).

Maybe the slightly related issue [#163](https://github.com/iiasa/message_ix/issues/163) could also be handled simultaneously with this one.

> Please advise on whether to run `black` here which results in a large diff ~Hm, possible we can create a new PR where we run `black` in the whole...

> Please advise on whether to run `black` here which results in a large diff I just see your branch is out of date with master, I guess a rebase...

> See also [“Versioning and locking”](https://github.com/iiasa/ece/wiki/Versioning-and-locking) in the (old) ECE GitHub wiki (this page [was not migrated](https://wiki.ece.iiasa.ac.at/wiki/index.php?search=Versioning+and+locking&title=Special%3ASearch&go=Go) when the ECE MediaWiki was set up). This is now migrated, please see...

> Thanks! In the old/GitHub wiki, I replaced the migrated content with a link to the new location, so there is no confusion. Thank you! Did the same [here ](https://github.com/iiasa/ece/wiki/Simplifying-the-ixmp-data-model)...

The utility method `iter_parameters()` got moved upstream from message_data to message-ix-models by commit https://github.com/iiasa/message-ix-models/commit/4d357025db72ec7b3d3bd5add9d19ed4f66e7cf4.