src/core/ns.js

var d3_nsPrefix = {
  svg: "http://www.w3.org/2000/svg",
  xhtml: "http://www.w3.org/1999/xhtml",
  xlink: "http://www.w3.org/1999/xlink",
  xml: "http://www.w3.org/XML/1998/namespace",
  xmlns: "http://www.w3.org/2000/xmlns/"
};

d3.ns = {
  prefix: d3_nsPrefix,
  qualify: function(name) {
    var i = name.indexOf(":"),
        prefix = name;
    if (i >= 0) {
      prefix = name.substring(0, i);
      name = name.substring(i + 1);
    }
    return d3_nsPrefix.hasOwnProperty(prefix)
        ? {space: d3_nsPrefix[prefix], local: name}
        : name;
  }
};