wiki: no released version was ever PolyForm Verified with git: v5.0.0's LICENSE and composer.json are MIT; the switch to PolyForm landed after that tag and was never tagged. The Licensing page now says that instead of implying a released licence change.
wiki: v6.0.0 and the Licensing page Version badges, footer and test counts move to 6.0.0 / 391 tests; the new Licensing page states what MIT allows, the one condition, what it does not grant, which artefacts it covers, and how tests/cases/16_release_contract.test.php keeps licence and version from drifting apart again. Also: broken TOC anchor on Expressions and Math, unlabelled code fences tagged.