[uf-discuss] hatom tumblr theme

Toby A Inkster mail at tobyinkster.co.uk
Mon Dec 15 06:23:42 PST 2008

James Tindall:

> Incidentally however, this vcard validator now complains that uid  
> should
> not appear twice on a page with the same value?
> http://hcard.geekhood.net/?url=microformats.tumblr.com

There is no prohibition on reusing UIDs in the hCard spec, but  
hcard.geekhood.net goes far beyond the spec with regards to  
suggesting best practices and things you might have missed. In  
general, I think it's a good tool, but in this case I (personally)  
disagree with it.

If Joe has an hCard for himself on his index.html and another hCard  
for himself on his contact-me.html, then nobody would think twice  
about giving them both the same UID. So if two hCards on different  
pages can have the same UID, then why not two hCards on the same  
page? What is important (and again this is just my opinion) is that  
if two hCards do have the same UID (whether they're on different  
pages or the same page), then they should be referring to the same  
contact (person, organisation, place, whatever).

To back up my argument, I'll cite the vCard spec (RFC 2426) which  
defines the purpose of "UID" as:

> To specify a value that represents a globally unique
> identifier corresponding to the individual or resource
> associated with the vCard.

That is, the UID is a unique identifier for the contact, not a unique  
identifier for the card.

I've contacted Kornel about this warning message and suggested that  
he change it so that the warning is only issued if two hCards have  
the same UID but different FNs.

As an aside, I'll point out that I do *not* recommend using the same  
UID for the historic hCards in a resume, because in that situation,  
merging details is not the desired behaviour - you want them to be  
kept separate.

Toby A Inkster
<mailto:mail at tobyinkster.co.uk>

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