Using XSl:Variable and XSL:if together.

Hi,

I want to declare a variable and use it in if statement.
I'm trying as follows.

        <xsl:variable name="chkValue" select="'true'"/>
        
        <xsl:if chkValue="true">
        
        --perform some operation.
        
        Change the value of variable name chkValue.     
        <xsl:variable name="chkValue" select="'false'"/>
        
        </xsl:if>

Please let me know where I'm going wrong in above implementation.

Thanks and regards,
Animesh