During the lead paragraph work we began a refactor of the MobileFormatter class for best testability and readability.

Code coverage of the new transforms is good:
https://doc.wikimedia.org/cover-extensions/MobileFrontend/transforms/index.html
https://doc.wikimedia.org/cover-extensions/MobileFrontend/MobileFormatter.php.html

Work (incomplete)

• Separate the LazyLoadedImages transform from MobileFormatter (https://gerrit.wikimedia.org/r/448415)
• Separate the LazyLoadedReferences transform from MobileFormatter
• Separate the LegacyMainPage transform from MobileFormatter (https://gerrit.wikimedia.org/r/#/c/401786/)
• Separate out the RemoveImages transform from MobileFormatter
• Separate out the SectionWrapping transform from MobileFormatter
• Review remaining transforms and their purpose (are they redundant?)
• Add tests for AddMobileTocTransform
• MobileContext contains many methods which should be migrated to the MobileFormatter - for example, [get|set]ContentTransformations. Review and port as appropriate