I have onmouseover/onmouseout event templates that show/hide a menu icon in context with the <p/> that the mouse is hovering over.  If the mouse leaves the window, I get the exception:

XPathException in mode: '{http://saxonica.com/ns/interactiveXSLT}onmouseout' event: '[object MouseEvent]: JavaScriptException in ixsl:call(): Object does not support property or method 'onMouseOutParagraph' with 2 argument(s). 

The template reads:

    <xsl:template match="p" mode="visibilityButtons">
        <xsl:param name="value"/>
        <xsl:for-each select="span[@class='menu']">
            <ixsl:set-attribute name="style:visibility" select="$value"/>
        </xsl:for-each>
        
        <xsl:choose>
            <xsl:when test="$value='hidden'">
                <xsl:variable name="isDifferentParagraph" select="ixsl:call(ixsl:window(),'onMouseOutParagraph',ixsl:event(),.)"/>
                <xsl:if test="$isDifferentParagraph">
                    <xsl:for-each select="span[@class='menu-contents']">
                        <ixsl:set-attribute name="style:display" select="'none'"/>
                    </xsl:for-each>
                </xsl:if>                    
            </xsl:when>
        </xsl:choose>        
    </xsl:template>

The function onMouseOutParagraph determines if I'm still hovering over the same paragraph or a different one, since entering/exiting <span/>s within the paragraph cause mouseout/mouseover events on the paragraph and I only want to hide the menu contents if the mouse has moved outside the paragraph boundaries.  It all works fine if the mouse stays within the bounds of the window.