4D v6.5 saw the implementation of a new type of object -- the splitter. A splitter divides a form into two areas, allowing the user to enlarge and reduce the areas by moving the splitter one way or the other. A splitter can be either horizontal or vertical.
Splitters are commonly used in list forms to allow the user to drag columns to different widths.
If you use 4D's form editor to create a new list form then 4D will automatically place a splitter object between each field and field title and will set the object properties of each field to allow it to grow/shrink in the appropriate direction.
You can alter the splitter's attributes using the Object Properties dialog to modify its appearance.
Splitters do not work in the User Environment or in subforms.