Thread:Extension talk:MassMessage/Incompatible with existing recipient list format/reply

The parserfunction is one of the few places where backwards compatibility was broken. The main design constraint for this was supporting global messages in a not-super-complicated way.

External links and interwiki links didn't work cleanly, so the easiest way to have users add structured data to a page was with a parser function. For local deliveries we could have added in allowing "User:"/"User talk:" links to work, however it would be a weird user experience if that worked on enwiki, but you had to use a special format to make it work on Meta. The parser function also enables us to display errors if a user provides invalid input.

For migrating existing lists, it should be possible to fix most of them with a simple find/replace regex. Ideally there should be some kind of wrapper template so that in case the backend does switch in the future, migrating will be less painful.