I have also been able to reproduce the issue (see screenshot example below). We can discuss if there is anything we can do about it at the next estimation.

I think the bigger question here is why this error is not appearing in the wiki page itself: https://en.wikisource.org/wiki/The_City_of_Dreadful_Night_and_other_poems/The_City_of_Dreadful_Night

That page has {{smallrefs|group="errata"}} which resolves to <references group="errata" />, so everything should be fine (and is fine, on wiki).

Could this be a Parsoid-Rendering bug?

The references list is being done via the {{smallrefs}} template, which calls {{#tag:references|{{{refx|}}}|group={{{group|}}}}}

@ssastry this looks like another Parsoid difference in rendering.

Ok, so, there are two distinct issues here:

• Legitimate wikitext issues which Parsoid flags as errors. If WS-Export doesn't want to display them, you should strip them from the output. They all have a typeof="mw:Error" property. See https://www.mediawiki.org/wiki/Specs/HTML/2.2.0#Error_handling and https://www.mediawiki.org/wiki/Specs/HTML/2.2.0/Extensions/Cite#Error_representation for Cite-specific errors. But, if you simply suppress nodes with typeof="mw:Error" property during WS-Export, you are good to go. There is nothing to do on the Parsoid end here.
• Parsoid bugs where some piece of wikitext is not being parsed identically to the core parser. We will take a look at errors like these.@Samwilson, do you know if the error reported here is seen on other pages as well? Or is this somehow specific to this one page?

Hope that helps.

The error is happening in the same form on https://en.wikisource.org/wiki/Paradise_Regained/Book_1

The error is that "no corresponding <references group="errata"/> tag was found", but there's a template at the end of that page, {{smallrefs|group="errata"}}, which resolves to {{#tag:references|{{{refx|}}}|group={{{group|}}}}}. This seems like it should work, and it is working correctly with the old parser.

I've tried to replicate this on Beta Wikisource. I haven't figured out how to get the error message, but have a look at this page and its Parsoid output. The last test case shows the references list failing to be displayed — I think this is the same error, but just without showing the error message.

It looks like the error has something to do with the fact that the <ref /> is transcluded by the ProofreadPage <pages /> tag. I think PRP is just doing basically '{{:' . $pageName . '}}' so I don't know why it'd be different from the 3rd test case above, but obviously something is changed.