code: public void execute(TransformerImpl transformer) throws TransformerException
    {
  
      XPathContext xctxt = transformer.getXPathContext();
      int sourceNode = xctxt.getCurrentNode();
  
        if (m_test.bool(xctxt, sourceNode, this)) {
            transformer.executeChildTemplates(this, true);
        }
  
    }
docs: Conditionally execute a sub-template.
  The expression is evaluated and the resulting object is converted
  to a boolean as if by a call to the boolean function. If the result
  is true, then the content template is instantiated; otherwise, nothing
  is created.
  
  @param transformer non-null reference to the the current transform-time state.
  
  @throws TransformerException