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 [5] https://html.spec.whatwg.org/multipage/semantics.html#attr-link-rel -- *Isabelle Hurbain-Palatin* (she/her) Senior Software Engineer Wikimedia Foundation <https://wikimediafoundation.org/>