The requirement is slightly more complicated than the ticket subject suggests -- it requires two headings. They don't have to be directly adjacent, but your selection has to start at the beginning of one heading, then extend over a separate heading which is immediately followed by a table.

This produces a transaction which tries to remove everything but the opening [heading] tag, including the closing [heading] tag of the last heading, leaving the document unbalanced and so erroring.

Open tables.html in the demo page

Where's the demo page? What's it for compared to, say, editing on a test wiki?

Also un-assigning @DLynch since this hasn't been touched in nearly a year. :-)

It's in the standalone demo, outside of MediaWiki: https://doc.wikimedia.org/VisualEditor/master/lib/ve/demos/ve/desktop.html

Yeah, it's a really specific situation required to trigger it, so lower priority seems fair.

This came up in the production error logs. I believe it's the same:
https://logstash.wikimedia.org/app/kibana#/doc/logstash-*/logstash-2020.08.31/clienterror/?id=AXRGVH9E3_NNwgAUz86D

The exception is the same, but I don't think the cause is the same. The page being editing (ContentTranslated) in error logs was https://en.wikipedia.org/wiki/Marc_Fesneau, which doesn't have any tables.

We should file a separate task for the production error.

I can still reproduce this. In order to get the selection I had to drag over the first lines of text and then shift-right once to extend the selection from 1-21 to 1-22 (I couldn't do it with mouse alone).

• https://doc.wikimedia.org/VisualEditor/master/js/lib/ve/demos/ve/desktop-wikimediaui.html#!tables
• Firefox 91 on macOS.

Uncaught Error: Unbalanced set of replace operations found
    process ve.dm.TransactionProcessor.js:102
    commit ve.dm.Document.js:371