https://crh.wikipedia.org/wiki/Roma?useparsoid=0&variant=crh-cyrl
vs
https://crh.wikipedia.org/wiki/Roma?useparsoid=1&variant=crh-cyrl&parsoidnewlc=1
The Parsoid html is:
<a href="//crh.wikipedia.org/wiki/Special:FilePath/Roma-Stemma.png" class="new" title="Файл:Рома-Стемма.пнг"><span class="mw-file-element mw-broken-media" resource="./Fayl:Roma-Stemma.png" data-width="90" data-height="160">алт=Тугъра[д]</span></a>
and we can see that we're prepending the alt= (in cyrillic алт=) in the text we emit for broken media.
See also T423742: Parsoid doesn't handle `<td style<nowiki>=</nowiki>...>` correctly on crhwiki which has another example of an alt= prefix making it into the HTML.