Copy part of the file if some conditions are applied

Hi,

I want to copy some parts of the tree, under certains
conditions, for example:

    <tagA>
      <tagB type="single">
        <pred>R_DoInitiali__T__ation</pred>
      </tagB>
      <tagC>
        <tagD type="single">
          <pred>NavG__z__Box</pred>
          <const name="eq">
            <arg>halfSide</arg>
          </const>
        </tagD>
        <tagD>
          <pred>NavBox</pred>
          <const name="eq">
            <arg>halfSide</arg>
          </const>
        </tagD>
        <tagE type="single">
          <pred>NavGBox</pred>
          <const name="eq">
            <arg>halfSide</arg>
          </const>
        </tagE>
      </tagC>
    </tagA>

If <pred> in <tagB> contains the caracter 'z' then
nothing should be copy from the <tagA> (and that
<tagA> should not appear in the transformation).
Otherwise, I have to check if any <pred> tag inside
<tagC> contains 'z', in that case, I cannot copy
anyhing from the father tag (D or E). That is, the
transformation would be:

    <tagA>
      <tagB type="single">
        <pred>R_DoInitiali__T__ation</pred>
      </tagB>
      <tagC>
      <!-- The <tagD>  with NavG__z__Box value   is
not copy -->
       <tagD>
          <pred>NavBox</pred>
          <const name="eq">
            <arg>halfSide</arg>
          </const>
        </tagD>
       <tagE type="single">
          <pred>NavGBox</pred>
          <const name="eq">
            <arg>halfSide</arg>
          </const>
        </tagE>
      </tagC>
    </tagA>

Is important to mention that in case I have just one
<tagD> inside <tagC>, and that <tagD> contains 'z',
nothing including <tagA> should be copied. 

    <tagA>
      <tagB type="single">
        <pred>R_DoInitiali__T__ation</pred>
      </tagB>
      <tagC>
       <tagD>
          <pred>NavBox__Z__</pred>
          <const name="eq">
            <arg>halfSide</arg>
          </const>
        </tagD>
       </tagC>
    </tagA>

(The result for this <tagA> is blank. Nothing can be
copied).

I am using: the <copy> template as follows but I just
copy part of the tags, but not the completely <tagA>
when in <tagD> there is no 'z'. 

<xsl:template match="tagA">
  <xsl:choose> 
   <xsl:when test=" ... "> <!--Check if pred in tagB
does not contains 'z' -->
          <xsl:for-each select="tagB/*/pred">
            <xsl:choose> 
             <xsl:when test=" ..."> <!--Check if pred
inside tagD  does not contains 'z' -->
                <xsl:copy> 
                  <xsl:apply-templates select=" @* |
node()"/> <!--This only copy tagD/E, but I also want
tagA and tagB -->
                </xsl:copy>
             </xsl:when>
            </xsl:choose>
       </xsl:for-each>    
   </xsl:when>
 </xsl:choose>
</xsl:template> 

Can anyone help me? 
Sorry for the long e-mail. 
Maria

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