Can WebM already be called an open standard?

[Timo Juhani Lindfors]

Hugo Roy <hugo at fsfe.org> writes:
> For PDF, yes, it is an open standard: see for instance
> http://pdfreaders.org

That lists multiple incomplete implementations of PDF. Point
http://fsfe.org/projects/os/def.en.html of requires multiple complete
ones and has many more points. Mostly I'm interested in getting
information on how PDF passes point 4.