WMLScript is a client side script language based on ECMAScript. It might seem a lot like JavaScript, and in a very general way it is meant for the same type of application which is to actually run simple code on the client side rather than just render a display which is the job of the markup language. WMLScript has obviously been modified to fit the limitations of the WAP environment.

This FAQ features a whole growing WMLscript section which starts here.

Chapter 6 in "Professional WAP" from Wrox