Many users suggested features, which were in turn inviting for the integration of wdiff into GNU diffutils. Collaboration proved to be rather difficult. After a few years, the wdiff author finally gave in and created mdiff as a way to break out of the situation and for becoming able to proceed with users' suggestions.
Before mdiff and the new wdiff2 based on it were
officially released, the original author resigned maintainership.
The new maintainers had little experience with the code, and therefore
decided to mark it experimental. That way, the code wouldn't be lost,
but it would be clear that it wasn't as testes as the good old