User blog comment:MisterWoodhouse/Social Activity, the 2010 Editor, and Unpausing Migrations/@comment-1967967-20200930115232/@comment-26939652-20200930151557

Ack, sorry about that. I saw two closing spans so figured I was good, but a third was opened that I missed.

If only VE source editor could do proper syntax highlighting for errors...

If a tag isn't closed in classic, you'd see the rest of the page as still "in a tag" and would eventually notice.