Positioning block-container inside margin of current page

Hi,

I need to add a block-container within the flow of an xsl template, but I
need to be able to position it at the page edge not the margin edge.
Positioning it at 0 positions to the margin edge.  How do I position it at
the page edge.  I assume a negative coordinate would do this, but how do I
get the margins for the current page of the flow.

TIA

Mark Williams