XPath expression for book title

Looking for an XPath expression that will give me the title of my book.

I want the title element of my book reproduced in the running headers. In the header.content template in my customisation layer I've been trying variations of

<xsl:value-of select="/bookinfo/title"></xsl:value-of>
<xsl:apply-templates select="/bookinfo/title" />

but get an empty result. 

The document is modular: a short master document includes a series of article documents. Is that changing the reference of the document root? If so, then 

<xsl:value-of select="/artheader/title"></xsl:value-of>

would yield my article titles in the headers. But that doesn't happen either.

Using ns-1.74.0 stylesheets, FOP (Xalan) for XSLT, XEP for FO processing.

Stephen Taylor