Last week, `nativeGalleryEnabled` was enabled in production https://gerrit.wikimedia.org/r/c/operations/mediawiki-config/+/889257
Running rt testing this week reported a number semantic differences when serializing from html instead of from data-mw,
https://parsoid-rt-tests.wikimedia.org/regressions/between/eced3e2/798eef3b
Note that selser will prevent any dirtying for unedited galleries and galleries edited by VE would drop the data-mw properties so there's no change to production. This is just about reporting during roundtrip testing but might yield some issues worth fixing.
---
`|thumb` media option dropped
ex. https://parsoid-rt-tests.wikimedia.org/resultFlagNew/eced3e2/798eef3b/jawiki/%E5%A4%A7%E5%88%86%E7%A9%BA%E6%B8%AF
This was known in T214601 and felt fine to normalize away since it isn't a valid media option in galleries. It seems like we can do better than the patch that was merged for that by having another argument to `renderMedia` that prevents other formats from rendering (first one wins T305628),
https://github.com/wikimedia/mediawiki-services-parsoid/blob/master/src/Ext/ParsoidExtensionAPI.php#L938-L946
In any case, the reason this is classified as a semantic difference is that the `alt` attribute on the `img` is suppressed for thumbs and not for plain floated images because the caption is visible for thumbs.
---
From https://parsoid-rt-tests.wikimedia.org/resultFlagNew/eced3e2/798eef3b/enwiki/MESSENGER_probe
```
------
ages of the spacecraft">
File:MESSENGER - Sonda.png|alt=Diagram of ''MESSENGER''|Diagram of ''MESSENGER''.
File:MESSENGER - installa
++++++
ages of the spacecraft">
File:MESSENGER - Sonda.png|alt=Diagram of MESSENGER|Diagram of ''MESSENGER''.
File:MESSENGER - installa
```
Here `|alt` formatting is lost. This can probably be fixed by T252246. The alt attribute is text though so the normalization seems fine.
The reason this is classified as a semantic difference is because the formatting in an attribute forces an `mw:ExpandedAttrs` typeof, which isn't there after roundtripping.
---
From https://parsoid-rt-tests.wikimedia.org/resultFlagNew/eced3e2/798eef3b/frwiki/Cormery
This seems to be because we're trimming the alt for the purpose of comparison with the caption but then using that for serialization. Should be fixable.
```
------
="packed" heights="150">
Cormery moulin6.jpg|alt= photograpgie en noir et blanc d'un bâtiment au dessus d'une rivière|<center>Moulin avant l'incendie de 1908.</center>
Cormery moulin3.jpg|alt=P
++++++
="packed" heights="150">
Cormery moulin6.jpg|alt=photograpgie en noir et blanc d'un bâtiment au dessus d'une rivière|<center>Moulin avant l'incendie de 1908.</center>
Cormery moulin3.jpg|alt=P
```
---
From https://parsoid-rt-tests.wikimedia.org/resultFlagNew/eced3e2/798eef3b/frwiki/Citro%D1%91n
The difference here seems to be that `WTUtils::textContentFromCaption` needs to strip non-breaking spaces before doing the comparison with the alt. Other entities probably need checking as well.
```
------
ains et ruraux|AMTUIR]].
Fichier:Citroën Type 23 - Coupe Florio 2013 (avant).jpg|thumb|Citroën Type 23.
Fichier:Belfégor.JPG|Camion Citroën type [[Citroën Belphégor|Belphégor]] 600 de 1966 : Poids vide : 4,610 T, PTAC 10,300 T.
</gallery>
==== Concept
++++++
ains et ruraux|AMTUIR]].
Fichier:Citroën Type 23 - Coupe Florio 2013 (avant).jpg|Citroën Type 23.
Fichier:Belfégor.JPG|alt=Camion Citroën type Belphégor 600 de 1966 : Poids vide : 4,610 T, PTAC 10,300 T.|Camion Citroën type [[Citroën Belphégor|Belphégor]] 600 de 1966 : Poids vide : 4,610 T, PTAC 10,300 T.
</gallery>
```
---
From https://parsoid-rt-tests.wikimedia.org/resultFlagNew/eced3e2/798eef3b/hewiki/%D7%A1%D7%A4%D7%A8%D7%98%D7%A7_%D7%9E%D7%95%D7%A1%D7%A7%D7%91%D7%94_(%D7%9B%D7%93%D7%95%D7%A8%D7%92%D7%9C)
Similar to thumb above, dimensions are dropped but, considering T305628, the gallery implementation should be updated to add its dimension last so that they are assured to be selected.
```
------
חק נגד צסק"א, עונת 2008.
קובץ:Spartak-Dinamo (7).jpg|250px|אוהד ספרטק — אוטו פישר, בן ה-102.
קובץ:Fratria perf.jpg|ארג
++++++
חק נגד צסק"א, עונת 2008.
קובץ:Spartak-Dinamo (7).jpg|אוהד ספרטק — אוטו פישר, בן ה-102.
קובץ:Fratria perf.jpg|ארג
```
---
Keep going ...