Re: variable question

If the relevant function call is the one shown, it means that the parent of
the mods:titleInfo context item is not a mods:relatedItem element, therefore
the function has been called with an empty sequence as the argument, which
is not allowed given the way you have declared the parameter.

    <relatedItem type="host">
      <titleInfo>
	<title>Newsweek</title>
      </titleInfo>

<xsl:function name="mods:reftype" as="xs:string">
  <xsl:param name="relatedItem" as="element(mods:relatedItem)" />
  <xsl:choose>
    <xsl:when test="$relatedItem/@type = 'host'">
      <xsl:variable name="issuance" as="xs:string"
        select="$relatedItem/mods:originInfo/mods:issuance" />
      <xsl:choose>
        <xsl:when test="$issuance = 'continuing'">article</xsl:when>
        <xsl:when test="$issuance = 'monographic'">chapter</xsl:when>
      </xsl:choose>
    </xsl:when>
    <xsl:otherwise>book</xsl:otherwise>
  </xsl:choose>
</xsl:function>

<xsl:template match="mods:titleInfo" mode="title-before">
  <xsl:if test="mods:reftype(parent::mods:relatedItem) = 'chapter'">
    <xsl:text>"</xsl:text>
  </xsl:if>
</xsl:template>