only parser xsl:include, header and footer not return ?

[zuojj]

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
	<xsl:template match="/a">
		<header>Header</header>
	</xsl:template>

	<xsl:include href="./src/template/a/a.xsl" />
	<xsl:template match="/b">
		<footer>Footer</footer>
	</xsl:template>
</xsl:stylesheet>