processing fo tags return from a java function

When i call the java function getPdfComment() that return a formated 
String with fo tags inside.
The result pdf don't process the fo tags : <fo:inline>coucou</fo:inline>
 

<fo:table-row>
        <fo:table-cell>
                <fo:block>
                        <useXsl:getPdfComment name="."/>
                        <xsl:value-of select="useXsl:getPdfComment(.)"/>
                </fo:block>
        </fo:table-cell>
        <fo:table-cell>
                <fo:block>
                        <fo:inline>COMMENTAIRE LIGNE 01</fo:inline>
                </fo:block>
        </fo:table-cell>
</fo:table-row>



static String getPdfComment(){
        return "<fo:inline>coucou</fo:inline>";
}

Does someone has an idea for processing fo tags return from a java 
function?

Didier