This attribute will be versioned and has requirements similar to Parsoid's data-parsoid attribute.

The RESTBase API will also need an update to fetch data-mw separately, and to store data-mw from the pagebundle response it receives from Parsoid for HTML version strings >= X.X.X (to be updated once this string is updated on the Parsoid end as part of T130638: Add data-mw as a separate JSON blob in the pagebundle output of Parsoid's API).