Getting the original context node while inside predicate

get at the original context item while inside a predicate.  Should  
there be an axis that allows you to go up the previous context items?

  	The typical use case for this is where you join two sets of nodes  
together based on a key.

<xsl:variable name="key"><xsl:value-of select="key"></xsl:variable>
<xsl:value-of "//otheritems[@key=$key]" />


	Besides cleaning up the above syntax it would make it possible to  
use in conjunction with <xsl:sort> (since you can't take a timeout to  
declare an <xsl:variable> before an <xsl:sort> at least in XSLT 1.0).