processing-instruction does not work within <link> tag

I am using libxml2-2.7.8 and docbook-xsl-1.78.1

In my customization layer, I have a processing instruction which consists of a simple text string:

<xsl:template match="processing-instruction('brand')">ABC</xsl:template>

and in my .xml I have a link:

<link linkend='my_section_id'>The brand is <?brand?></link>

In the pdf output link I see: "The brand is ABC"

but in the html link text I see "The brand is"

In most of the rest of the html output the instruction is being processed and <?brand?> is replaced by "ABC". 

Any ideas why the processing-instruction('brand') is not being processed within the <link> tag for the html output?

Thanks,

Flavia

-- 

Flavia Majlis, 
MSc, Computer Science, McGill University
BFA, Photography, Concordia University

www.flaviamajlis.com
cabinetphoto.org

www.simlog.com

1.514.909.6101