We are working on adding some Facebook Connect functionality to our site. Part of their requirements for FB Connect require adding several additional xmlns attributes to the html element. We are likely going to have 5 or 6 of their custom attributes by the time we’re done, and I want to know if this will negatively affect our page performance. I.e. will these be additional resources that the browser has to download?
I have checked in Firebug and I don’t see additional requests, but I don’t know if that is because requests are not made by the browser, or if Firebug simply doesn’t track them.
No. Namespace declarations are for identification only; take no more resources than storing any other attribute/value pair.
Although it is customary to use resolvable URIs for namespace identifiers, no XML processing tool will actually attempt to fetch that URI.