== Background
Historically code has used mw-message-box for styling message boxes.
As part of standardization to Codex, this markup must now be transitioned to CdxMessage markup:
https://doc.wikimedia.org/codex/latest/components/demos/message.html#markup-structure
If extensions are using Html::messageBox there is nothing to do here.
Extensions using JavaScript to create message box should either switch to Codex or alter their markup:
Currently to mitigate impact Vector 2022 skin loads the old styles via JavaScript but we would like to remove this in future.
== TODO
Impacted code https://codesearch.wmcloud.org/deployed/?q=mw-message-box and https://global-search.toolforge.org/?q=mw-message-box®ex=1&namespaces=&title=
Phase 1: updates to extensions
[] MobileFrontend
[] CentralNotice
[] Gadgets (user notice)
[] FlaggedRevisions
[] Graph
[] GrowthExperiments
[] MassMessage
[] TemplateData
[] TwoColConflict
Phase 2: dropping support
[] Remove loading of message box styles via JavaScript in Vector.
[] Remove loading of code in Minerva.
[] Update markup in core to remove references to old non-Codex classes.