From https://build.fhir.org/extension-derivation-reference.html

Clicking on "reference", "path", "offset" or "length" – all four go to https://build.fhir.org/extension-derivation-reference-definitions.html#extension.DerivationReference instead of to the element-specific section of the definitions page. Other extensions exhibit the same behavior (e.g. ,https://build.fhir.org/extension-cqf-targetinvariant-definitions.html#extension.targetInvariant)