Saxon

Using XML Editor 21.1, build 2019101513 and its in-menu Tools > Compile XSL Stylesheet for Saxon... command.

About > Libraries claims Saxon EE 9.8.0.12.

In preview the following XML code seems to be partially eaten by the render engine, so I've also attached them as files.

File 1: root.xsl

<xsl:transform
	expand-text="yes"
	extension-element-prefixes="ixsl"
	version="3.0"
	xmlns="http://www.w3.org/1999/xhtml"
	xmlns:ixsl="http://saxonica.com/ns/interactiveXSLT"
	xmlns:rh="urn:publicid:rh"
	xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

	<xsl:use-package
		name="urn:publicid:rh:second">
		<xsl:override>
			<xsl:template
				match="html/head/title"
				mode="rh:init">
				<xsl:result-document
					href="?."
					method="ixsl:replace-content">Root Title</xsl:result-document>
			</xsl:template>
		</xsl:override>
	</xsl:use-package>
</xsl:transform>

File 2: second.xsl

<xsl:package
	expand-text="yes"
	extension-element-prefixes="ixsl"
	name="urn:publicid:rh:second"
	package-version="1.0.0"
	version="3.0"
	xmlns="http://www.w3.org/1999/xhtml"
	xmlns:ixsl="http://saxonica.com/ns/interactiveXSLT"
	xmlns:rh="urn:publicid:rh"
	xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

	<xsl:mode
		name="rh:init"
		visibility="public" />

	<xsl:template
		name="xsl:initial-template"
		visibility="public">
		<xsl:message>start xsl:initial-template</xsl:message>
		<xsl:apply-templates
			mode="rh:init"
			select="ixsl:page()" />
		<xsl:message>exit xsl:initial-template</xsl:message>
	</xsl:template>

	<xsl:template
		match="html/head/title"
		mode="rh:init">
		<xsl:result-document
			href="?."
			method="ixsl:replace-content">Second Title</xsl:result-document>
	</xsl:template>

</xsl:package>

File 3: saxon.conf.xml:

<configuration
	edition="EE"
	label="SaxonJSUI"
	xmlns="http://saxon.sf.net/ns/configuration">
	<xsltPackages>
		<package
			name="urn:publicid:rh:second"
			sourceLocation="file:/ ...elided... /rh.library/xsl/second.xsl"
			version="1.0.0" />
	</xsltPackages>
</configuration>

On compiling root.xsl, I get the error Cannot find a 0-argument function named {http://saxonica.com/ns/interactiveXSLT}page()

Installing the Saxon 9.9 add-on and using the toolbar Compile XSLT Saxon 9.9 does, however, succeed.