I added this to https://www.mediawiki.org/wiki/Extension:EventLogging/Guide#QA .
Is there a way the guide can transclude someone's "master" copy of the JS into a <source> tag so it remains up-to-date? Or vice-versa, can developers do a labelled transclude of a code snippet from wikitext into their own user JS? [1]

I clicked a link in a TOC on testwiki and a yellow section appeared
undefined] Missing property "action"
[undefined] Value null is the wrong type for property "duration" (integer expected)
\o/ !  But I had no idea what this was, so maybe a badge or header "EventLogging validation error" that links to https://www.mediawiki.org/wiki/Extension:EventLogging/Guide#QA would be useful.

(I filed a bug against Popups which is logging  this, https://phabricator.wikimedia.org/T86378 )

[1] Another fine topic for the MW Developer Summit 2015 documentation session, come with ideas, enjoy pastries!

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=S Page  WMF Tech writer