Netbeans version used: netbeans-trunk-nightly-200708061200-full.zip

The editor mandates that the newly created .xsl file should always have a default template.

The 'orderToCustTransform.xsl' when created has a default root template defined.

	<xsl:template match="/">
	</xsl:template>

Since the editor does not yet support template creation, manually changing this to have default templates as shown

    <xsl:template match="ns:Orders">
        <CustomerHistoryEntries xmlns="http://xml.netbeans.org/schema/custhistory"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://xml.netbeans.org/schema/custhistory custhistory.xsd">
            <xsl:apply-templates/>
        </CustomerHistoryEntries>
    </xsl:template>

leads to error message in the design view 
"The XSLT file does not contain a root template element"

It is not mandatory that a .xsl file should contain a root template element.