The main observable difference between a string and this RTF is the effect
of boolean(). Converting a string to a boolean gives true unless the string
is empty. Converting an RTF to a boolean always gives true.

So
<xsl:param name="hyphenate">true</xsl:param> is true and
<xsl:param name="hyphenate">false</xsl:param> is also true?
So <xsl:param name="hyphenate" select="'false'"/> is the right way?