Change #1064069 had a related patch set uploaded (by Subramanya Sastry; author: C. Scott Ananian):

[mediawiki/services/parsoid@master] Prefer literal string image option to prefixed image option

https://gerrit.wikimedia.org/r/1064069

Some more information:

> $services = \MediaWiki\MediaWikiServices::getInstance();
> $l = $services->getLanguageFactory()->getLanguage('eo');
> $mwf = new \MediaWiki\Parser\MagicWordFactory($l, $services->getHookContainer());
> $x = $mwf->newArray(['img_left','img_width']);
> $x->getBaseRegex();
= [
    "(?i:(?!))",
    "(?P<a_img_left>maldekstra)|(?P<b_img_left>maldekstre)|(?P<c_img_left>left)|(?P<a_img_width>\$1ra)|(?P<b_img_width>\$1px)",
  ]
> $x->matchVariableStartToEnd('maldekstra');
= [
    "img_left",
    false,
  ]
> $x = $mwf->newArray(['img_width','img_left']);
> $x->getBaseRegex();
= [
    "(?i:(?!))",
    "(?P<a_img_width>\$1ra)|(?P<b_img_width>\$1px)|(?P<a_img_left>maldekstra)|(?P<b_img_left>maldekstre)|(?P<c_img_left>left)",
  ]
> $x->matchVariableStartToEnd('maldekstra');
= [
    "img_width",
    "maldekst",
  ]

Note that the precedence of options is pretty much arbitrary, it just *happens* that img_width is added after other options. Parsoid is a bit more principled here, always preferring literal parameters to parameterized (prefix) parameters.

Although the possibility for conflicts exists for all parameterized image parameters, the img_width parameter is the most likely one to result in conflicts in actual practice. Most other parameterized arguments include = in the pattern, which is not likely to occur in a parameter literal, although eg (from MessagesEo.php):

	'img_page'                  => [ '1', 'paĝo=$1', 'paĝo $1', 'pagxo=$1', 'pagxo_$1', 'page=$1', 'page $1' ],

it's not impossible that someone could define a different image parameter as something like page left which would conflict with img_page in the same way that img_width conflicted with img_left for Esperanto.

Anyway, I have a patch to reorder the parameter names in the legacy parser to try to minimize the chance of these issues, and I think Parsoid's policy of always preferring literal parameter names to parameterized names is a reasonable and principled policy for the future.

Change #1064408 had a related patch set uploaded (by C. Scott Ananian; author: C. Scott Ananian):

[mediawiki/core@master] Clarify precedence between conflicting localized image parameter names

https://gerrit.wikimedia.org/r/1064408

Change #1064409 had a related patch set uploaded (by C. Scott Ananian; author: C. Scott Ananian):

[mediawiki/core@master] Add `double-px-category` tracking category for deprecated image size syntax

https://gerrit.wikimedia.org/r/1064409

Change #1064069 merged by jenkins-bot:

[mediawiki/services/parsoid@master] Prefer literal string image option to prefixed image option

https://gerrit.wikimedia.org/r/1064069

Change #1064408 merged by jenkins-bot:

[mediawiki/core@master] Clarify precedence between conflicting localized image parameter names

https://gerrit.wikimedia.org/r/1064408

Change #1066683 had a related patch set uploaded (by Isabelle Hurbain-Palatin; author: Isabelle Hurbain-Palatin):

[mediawiki/vendor@master] Bump wikimedia/parsoid to 0.20.0-a18

https://gerrit.wikimedia.org/r/1066683

Change #1066683 merged by jenkins-bot:

[mediawiki/vendor@master] Bump wikimedia/parsoid to 0.20.0-a18

https://gerrit.wikimedia.org/r/1066683

Change #1064409 merged by jenkins-bot:

[mediawiki/core@master] Add `double-px-category` tracking category for deprecated image size syntax

https://gerrit.wikimedia.org/r/1064409