Can an implementation define extension command, event, or property names?

[gsnedders]

The spec currently says:

An implementation may define extension modules. These must have a module name that contains a single colon ":" character. The part before the colon is the prefix; this is typically the same for all extension modules specific to a given implementation and should be unique for a given implementation.

Other specifications may define their own WebDriver-BiDi modules that extend the protocol. Such modules must not have a name which contains a colon (:) character, nor must they define command names, event names, or property names that contain that character.

Clearly an implementation may define extension modules whose name contains a colon, and other specifications cannot define module, command, event, or property names containing colons… but can implementations define command, event, or property names containing colons?