Does the W3C allow "reference implementations"?

["Costello, Roger L." <costello@mitre.org>]

Hi Folks,

I just read this:

    ISO officially does not allow reference implementations

Here's where I read it:

    http://www.schematron.com/implementation.html 

See the 2nd sentence of the 2nd paragraph.

The author of that web page is Rick Jelliffe, who is the author of several ISO standards.

This got me wondering, "Does the W3C allow reference implementations?"

I know that the W3C requires a specification have a certain number of implementations before the specification can become a full Recommendation. Does the W3C consider them to be "reference implementations"?

What is the rationale for not allowing reference implementations?

/Roger