Check if container element for publishing instructions exists XSLT

I was handling this processing instruction: <?Pub _kern Amount="-25pt"?>

with:

<xsl:template match="processing-instruction('Pub')">
        <xsl:choose>
            <xsl:when test="starts-with(., '_kern')">
                <xsl:attribute name="style"><xsl:text>padding-left: </xsl:text>
                <xsl:value-of select="if (contains(.,'Amount')) then (substring-before(substring-after(., 'Amount=&quot;'), '&quot;')) else '12pt'"/>
                </xsl:attribute>
            </xsl:when>
        </xsl:choose>
</xsl:template>

but this only works when the PI is inside a container element like <div>, etc. I received an error because the XSLT was trying to add a style tag to a non-existent parent element. If I include a <span> before the <xsl:attribute name="style"> then the code doesn't work when the PI is inside a container element. How can I detect whether there is a container element so I know whether or not to add a span? Unless there is a better way to do this, I'm a beginner with XSLT.