When working with the Content Query Web Part.

Export then editing the Web part to use custom fields

<property name="CommonViewFields" type="string">CustomField1, Text;CustomField2, Number;</property>

Output all available parameters in the ItemStyle.csl

<ul>
 	<li>Specific Variable: <xsl:value-of select="$SafeImageUrl"></xsl:value-of></li>
 	<li>Specific Parameter: <xsl:value-of select="@SafeImageUrl"></xsl:value-of></li>
 	<xsl:for-each select="@*">
	    <li>P:<xsl:value-of select="name()" /></li>
	</xsl:for-each>
 </ul>

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