content key replaces purge in Tailwind CSS v3 with deprecation warning

Tailwind CSS v3 introduced the content configuration key to replace the legacy purge key, with the old key still accepted but emitting a deprecation warning ahead of removal in a future major release.

A migration plan needs to move file globs and safelist entries from purge to content while maintaining consistent class generation across builds. The configuration transition is complicated by backward compatibility that falls back to purge when content is absent, and by the relocation of safelist under content.

There is uncertainty about the interaction when both keys are present during a gradual change.

Does Tailwind merge the globs from content and purge or prioritize one source? Are safelist entries defined under the legacy purge key still honored after the move? What configuration shape avoids duplicate scanning while keeping the deprecation warning clear during transition?