Description of the bug:

register_toolchains is documented twice with slightly different documentation text.

https://bazel.build/rules/lib/globals#register_toolchains() is the permalink to both. If you visit that link you'll see both items. One reads "Register an already-defined toolchain..." and the other "Specifies already-defined toolchains...".

register_execution_platforms() and repository_rule(implementation, attrs, local, environ, configure, remotable, doc) are also duplicated.