Re: newbie variable question

if there are any grp/type element whose contents are "DMA" I want to
print out the value of the associated name in that grp.  if there is no
grp/type element whose contents is "DMA" I want to print out the values
of the description element.
[XML:]
    <area>
       <grp>
         <type>MSA</type>
         <name>foo</type>
       </grp>
       <grp>
         <type>DMA</type>
         <name>bar</type>
       </grp>
     </area>
     <description>baz</description>

[XSLT:]
  <xsl:for-each select="area/grp">
    <xsl:if test="string(type)='DMA'">
      <xsl:value-of select="name"/>
     <xsl:variable name="ValueExists" select="'True'"/>
    </xsl:if>
  </xsl:for-each>
<xsl:if  test="$ValueExists!="'True'">
 <xsl:value-of select="description" />
</xsl:if>

but I keep getting an error:

A reference to variable or parameter 'ValueExists' cannot be resolved.
The variable or parameter may not be defined, or it may not be in scope.

   Begin for-each....
     If some condition....
       Define variable $ValueExists
     End if
   End for-each

   If some condition....
     Do something with $ValueExists
   End if