Given the current url, we'd like to display/hide a button

[Webmaster]

Given the current displayed url, we would like to display or hide a
button on the toolbar.

By using <INCLUDE_XML>, it looks like I can have a custom script called
on BeforeNavigate or OnDocumentComplete. I can send the %url value to the server script so it can detect whether or not the button should be
add to the toolbar, to taken away.

My question is: what is the script returning so that this button is
added or removed?

[Admin]

You can add CustomXML to your toolbar and use javascript toolbar
method: CustomXML()

Here is an example on javascript:

if(...)
{//right url - adding buttons
MyTool.CustomXML("CustomXML1") = '<TOOLBAR><BUTTON
id="tbs_button_007132" caption="MyButton" visibility="1"
type="Split" command="MyCommand" img="52" hint="MyHint"/></TOOLBAR>';
}
else
{//not right url - remove buttons
MyTool.CustomXML("CustomXML1") = '<toolbar></toolbar>';
}