detecting text between nodes

dear xsl-specialists,

i try write an xsl to transform html-documents (with a restricted
html-subset) directly to fo.

my only problem is the <br/>-tag:
if i have "aaa<br/>bbb<br/>ccc"
then i simply have to replace each br-tag with a <fo:block/> just to insert
a line-break.

but if i have "aaa<br/><br/>bbb" the first br is responsible for the
line-break and the second will insert an empty line, i.e. i have to convert
the second br-tag to something that inserts an empty line:
"aaa<fo:block/><fo:block space-after="10"/>bbb"

so, the attribute "space-after=10" is present if the preceding sibling is a
"br" and there is nothing except whitespace between the current br and the
preceding br;

but how can i express this condition with xpath?

<xsl:template match="br">
  <fo:block>
    <xsl:if test="name(./preceding-sibling::*[1])='br' and
NOTHINGBUTWHITESPACEBETWEEN(.,./preceding-sibling::*[1])">
      <xsl:attribute name="space-after">10pt</xsl:attribute>
    </xsl:if>
  </fo:block>
</xsl:template>


tia for any hint!

fusel!