can I *undefine* an attribute via xsl:attribute?

Hi all,

I would like to call a template that creates various attributes, then
conditionally *undefine* certain attributes, using some **MAGIC** below:

<xsl:template name="create-my-attributes>
  <xsl:call-template name="create-their-attributes"/>
  <xsl:attribute name="unwanted-attribute" select=**MAGIC**/>
</xsl:template>

A later xsl:attribute definition overrides an earlier value. But can I somehow
define an attribute as "undefined" to uncreate it? The spec at

https://www.w3.org/TR/xslt-30/#creating-attributes

doesn't mention this as an option, but I'm a novice and perhaps I missed
something.

Thanks!

-----
Chris Papademetrious
Tech Writer, Implementation Group
(610) 628-9718 home office
(570) 460-6078 cell