YES, it works, it's elementary logic i forgot to put it into weight. Thanks Stephan. Can I make an additional question?

In my table I also have some integet columns with number. At the bottom of the table I add a row and sum these columns. I use the following code:

          <tr >
            <td>
              Total
            </td>
            <xsl:for-each select="//udt:Fields">
              <xsl:if test="udt:Visible='true' or udt:Visible='True'">
                <td>
                  <b>
                    <xsl:variable name="NameOfValueColumn" select="udt:ValueColumn"/>
                    <xsl:value-of select="sum((.|preceding-sibling::udt:Data)/*[name()=$NameOfValueColumn])" disable-output-escaping="yes"/>
                  </b>
                </td>
              </xsl:if>
            </xsl:for-each>
          </tr> 

The problem now is that it sums all the available rows. How can I sum up only the filtered rows?

FINALLY I figured out the correct syntax! For those who may find the article useful, the syntax is:

<xsl:value-of select="sum((.|preceding-sibling::udt:Data[udt:UserN=//udt:Context/udt:UserName or //udt:Context/udt:UserName='tate' or /udt:UserDefinedTable/udt:Context/udt:IsAdministratorRole = 'true'])/*[name()=$NameOfValueColumn])" disable-output-escaping="yes"/>

The next challange for me is to make the search available only for Admin user. The problem is not only the visablibliy of the control but the removal of filteredData:

contains(*[name()=$searchColumns][1],$search) or contains(*[name()=$searchColumns][2],$search) or contains(*[name()=$searchColumns][3],$search) or contains(*[name()=$searchColumns][4],$search) or contains(*[name()=$searchColumns][5],$search)or contains(*[name()=$searchColumns][6],$search)or contains(*[name()=$searchColumns][7],$search)or contains(*[name()=$searchColumns][8],$search)or contains(*[name()=$searchColumns][9],$search)or contains(*[name()=$searchColumns][10],$search)

Can you pass me hints how to deal with this situation?