I'm using the following stylesheet to merge adjacent nodes of a
particular type and sum their attributes:

<?xml version="1.0" encoding="UTF-8" ?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:aston="http://www.aston.tv/schemas/Aston/Aston7">

  <xsl:template match="node()">
      <xsl:copy>
          <xsl:copy-of select="@*"/>
          <xsl:apply-templates select="node()[1]"/>
      </xsl:copy>
      <xsl:apply-templates select="following-sibling::node()[1]"/>
  </xsl:template>

  <xsl:template match="aston:offset[not(node())]">
      <xsl:param name="a" select="/.."/>
      <xsl:choose>
          <xsl:when test="following-sibling::node()[self::* or
normalize-space(.)][1]/self::aston:offset[not(node())]">
              <xsl:apply-templates
select="following-sibling::aston:offset[1]">
                  <xsl:with-param name="a" select="$a|@*"/>
              </xsl:apply-templates>
          </xsl:when>
          <xsl:otherwise>
              <offset xmlns="http://www.aston.tv/schemas/Aston/Aston7"
x="{sum($a[name()='x']|@x)}" y="{sum($a[name()='y']|@y)}"
z="{sum($a[name()='z']|@z)}" />
              <xsl:apply-templates select="following-sibling::node()[1]"/>
          </xsl:otherwise>
      </xsl:choose>
  </xsl:template>

<text>
  Hello<offset x="2" y="4" /><offset x="3" y="2" />World
</text>

<text>
  Hello<offset x="5" y="6" />World
</text>

My problem occurs if I have a whitespace character between the two
adjacent nodes, like so:

<text>
  Hello<offset x="2" y="4" /> <offset x="3" y="2" />World
</text>

In this case, I wouldn't expect the nodes to be merged as they're not
strictly adjacent (there's a whitespace node between them) - but they are!