Building on a previous post Oracle “Is Numeric” a similar thing is possible using XSLT (or more accurately, XPATH) too…
<xsl:if test="string-length(translate(node(),' +-.1234567890', ' ')) > 0"> <xsl:text>not numeric</xsl:text> </xsl:if>
Not exactly ground breaking stuff, but something similar did turn out useful for extracting the non numerical area component of a post code (i.e. the SO bit of SO53 3RY).
Which I thought was close enough to the oracle is numeric implementation to make comment.