Caveat - xlink:href in ISO 19139 Geographic Metadata

I wanted to use the same instances of gmd:authority/gmd:CI_Citation
many times, so I came up with using xlink:href.

[definition]
<gmd:authority>
<gmd:CI_Citation id="url.authority">
<gmd:title>...
</gmd:CI_Citation>
</gmd:authority>

[quotation]
<gmd:authority>
<gmd:CI_Citation xlink:href="#url.authority">
</gmd:authority>

But it causes validation error, saying xlink:href is not allowed in CI_Citation.
It took a while, but finally I got the reason reading XML schema.

The xlink:href attribute must be attached to parent element of omitted
element that would be if xlink:href is not used.
So following validates.

<gmd:authority>
<gmd:CI_Citation id="url.authority">
<gmd:title>...

<gmd:authority xlink:href="#url.authority"/>