Conditionally set attribute in JSPX element.

attribute.tagx

<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page" version="2.1" 
	xmlns:c="http://java.sun.com/jsp/jstl/core">
	<jsp:output omit-xml-declaration="yes"/>
	<jsp:directive.attribute name="name" type="java.lang.String" required="true" rtexprvalue="true" description="Name"/>
	<jsp:directive.attribute name="value" type="java.lang.String" required="true" rtexprvalue="true" description="Value"/>
	<jsp:scriptlet>
	//<![CDATA[
	           String name = (String) jspContext.getAttribute("name");
	           String value = (String) jspContext.getAttribute("value");
	           out.write(" " + name + "=" + "\"" + value + "\"");
	//]]>
	</jsp:scriptlet>
</jsp:root>

element-end.tagx

<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page" version="2.1" 
	xmlns:spring="http://www.springframework.org/tags"
	xmlns:c="http://java.sun.com/jsp/jstl/core">
	<jsp:output omit-xml-declaration="yes"/>
	<jsp:directive.attribute name="name" type="java.lang.String" required="true" rtexprvalue="true" description="Name"/>
	<jsp:scriptlet>
	//<![CDATA[
	           String name = (String) jspContext.getAttribute("name");
	           if (name != null) {
	           		out.write("</" + name + ">");
	           }
	//]]>
	</jsp:scriptlet>
</jsp:root>

element-start.tagx

<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page" version="2.1" 
	xmlns:c="http://java.sun.com/jsp/jstl/core">
	<jsp:output omit-xml-declaration="yes"/>
	<jsp:directive.attribute name="name" type="java.lang.String" required="true" rtexprvalue="true" description="Name"/>
	<jsp:scriptlet>
	//<![CDATA[
		String name = (String) jspContext.getAttribute("name");
		out.write("<" + name);
	//]]>
	</jsp:scriptlet>
	<jsp:doBody />
	<jsp:scriptlet>
	//<![CDATA[
		out.write(">");
	//]]>
	</jsp:scriptlet>	
</jsp:root>

example.jspx

<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page" version="2.1" 
	xmlns:c="http://java.sun.com/jsp/jstl/core"
	xmlns:help="urn:jsptagdir:/WEB-INF/tags/help">
	<jsp:output omit-xml-declaration="yes"/>
		<spring:url var="baseUrl" value="/" />
		
<help:element-start name="div">
	<c:if test="${device.html5 }">
	<help:attribute name="data-position" value="fixed" />
	</c:if>
	<help:attribute name="data-role" value="header" />
</help:element-start>
Some stuff here and tags here...
<help:element-end name="div" />

Stick all the tagx files into the /WEB-INF/tags/help directory.

Then see example.jspx.