getting position of tag

Hi.

I have this problem:

XML:
<columns>
        <column>
                <source>A</source>
        </column>
        <column>
                <source>B</source>
        </column>
</xolumns>

I want to get position() of tag column, where source='B'.

I have tried
xsl:value-of select="/columns/column[source='B']/position()"
but it is bad.

Anyone help me?

Thanks.


-- 

Dusan Zatkovsky