From http://www.w3schools.com (Copyright Refsnes Data)

WMLScript How to

How to call a WMLScript from a WML page

Notice that WMLScripts are not embedded in WML pages. The WML pages only contains references to script URLs.

In the example below; if you select the go label the external script will direct you to http://www.w3schools.com/wap.wml:

<?xml version="1.0"?>
<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN"
"http://www.wapforum.org/DTD/wml_1.1.xml">

<wml>
<card id="no1" title="Go to URL">
<do type="options" label="Go">
<go href="check.wmls#go_url('W3Schools')"/>
</do>
</card>
</wml>

The red line above contains a reference to a WMLScript. The script is in a file called check.wmls, and the name of the function is go_url.

Here is the WML page called check.wmls:

extern function go_url(the_url)
{
if (the_url=="W3Schools")
{
WMLBrowser.go("http://www.w3schools.com/wap.wml")
}
}

Note that the function is using the extern keyword. When using this keyword the function can be called by other functions or WML events outside the .wmls file. To keep a function private, drop the extern keyword.