Dynamic blocks is a bit of a mystery to some. It has been around for ages but no one really knows how to get started. One of the easiest dynamic block commands to use is the stretch command. When using dynamic blocks there are 2 things that need to be applied. A parameter and an action.
To use the stretch parameter and action you create it just like you would if you were using the normal stretch command in AutoCAD. When you select your elements for the stretch command remember that if the drawing element is fully inside the crossing window it will be moved and if it is partially inside the crossing window it will stretch.