We stipulate that if a DocBook user uses callouts such
programlistingco, they must
have a subdirectory named
callout/ containing images named
2.png, and so forth, to be used as the
graphic for callouts 1, 2, ….
<!--callout.graphics.path: Location of the callout graphics--> <xsl:param name="callout.graphics.path">callouts/</xsl:param>