Blank nested if

A nested xsl:if inside another xsl:if can always be collapsed into one xsl:if by joining the conditions with and.

Incorrect:

<xsl:if test="$a">
  <xsl:if test="$b">
    <xsl:value-of select="."/>
  </xsl:if>
</xsl:if>

Correct:

<xsl:if test="$a and $b">
  <xsl:value-of select="."/>
</xsl:if>