Is this structure valid for a canonical tag?

[nicole.healthline]

Working on a site, and noticed their canonical tags follow the structure:

//www.domain.com/article

They cited their reason for this as http://www.ietf.org/rfc/rfc3986.txt. Does anyone know if Google will recognize this as a valid canonical? Are there any issues with using this as a the canonical?

[irvingw]

looks weird and i would fix personally,  but if you leave off http:  a URL does resolve.

look at the indexing on the site and see if the canonical rules are being followed since they are already implemented on the site.