Hello everyone,

As part of the effort to align Parsoid's output with the output of the legacy parser [1], we introduced a possibly backwards incompatible change [2] in the latest Parsoid version (0.17.0-a1, deployed along with 1.40.0-wmf.1).

Up until that version, while there was no guarantee that it was the case, the "rel" attribute of HTML tags only had a single value. In particular, it was possible to access all the external links of a page with `a[rel="mw:ExtLink"]`. We updated our known clients [3], but did not communicate that fact outside of the update of our Parsoid HTML specification [4].

Selectors relying on the "rel" attribute of Parsoid HTML should consequently be updated to take into account that they can (and do) now contain space-separated multi-values, as specified in the HTML Living Standard [5]. A list of what to check is provided in the client-side ticket [3]. In most cases, a selector like `a[rel=”mw:ExtLink”]` just needs a single character added: `a[rel~=”mw:ExtLink”]` will correctly match multi-valued rel attributes.

We apologize for the late communication and the inconvenience.

Best regards,

Isabelle, for the Content Transform Team

[1] https://phabricator.wikimedia.org/T186241

[2] https://gerrit.wikimedia.org/r/c/mediawiki/services/parsoid/+/822655 

[3] https://phabricator.wikimedia.org/T315209 

[4] https://www.mediawiki.org/wiki/Specs/HTML/2.6.0