createElementNS - how do I add attribute xmlns:xlink?

I see things like this on the net:

<svg
   xmlns               = "http://ift.tt/nvqhV5"
   xmlns:xlink         = "http://ift.tt/PGV9lw"
   >

I create my element in javascript with

var eltSvg = document.createElementNS("http://ift.tt/nvqhV5", "svg");

However looking at the element in Google Chrome I see no attribute "xmlns" and no attribute "xmlns:xlink".

I guess that "xmlns" somehow is there (since that part works), but now I need to use "xmlns:xlink".

Is it there? Is there some standard for putting it there on the svg element?