(dsssl) Adding a text the *first* time an element is seen

[Stephane Bortzmeyer <bortzmeyer@xxxxxx>]

I would like to add a small blurb in a document after a given element,
but only once, when the element first appears.

Here is how I do it in XSL:

<xsl:template match="rfc">
...
<xsl:if test="not(preceding::rfc)"> (RFC means Request For
Comments. They can be downloaded from 
<a href="http://www.rfc-editor.org/";>RFC editor</a>.) </xsl:if>
</xsl:template>

How can I do so with DSSSL?

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