An attribute can be placed in a namespace by prefixing its name.
Normally only used for global atributes that can appear on any element such as XLink attributes rather than attributes that are tied to a specific element.
Unprefixed attributes are never in any namespace.
Being an attribute of an element in the http://www.w3.org/1999/xhtml namespace is not sufficient to put the attribute in the http://www.w3.org/1999/xhtml namespace.
The only way an attribute belongs to a namespace is if it has a declared prefix, like xlink:type and xlink:href.
<xhtml:html xmlns:xhtml="http://www.w3.org/1999/xhtml"
xmlns:xlink="http://www.w3.org/1999/xlink">
<xhtml:head><xhtml:title>Three Namespaces</xhtml:title></xhtml:head>
<xhtml:body>
<xhtml:h1 align="center">An Ellipse and a Rectangle</xhtml:h1>
<svg:svg xmlns:svg="http://www.w3.org/2000/svg"
width="12cm" height="10cm">
<svg:ellipse rx="110" ry="130" />
<svg:rect x="4cm" y="1cm" width="3cm" height="6cm" />
</svg:svg>
<xhtml:p xlink:type="simple"
xlink:href="ellipses.html">
More about ellipses
</xhtml:p>
<xhtml:p xlink:type="simple" xlink:href="rectangles.html">
More about rectangles
</xhtml:p>
<xhtml:hr/>
<xhtml:p>Last Modified February 13, 2000</xhtml:p>
</xhtml:body>
</xhtml:html>