• Initial globals: Stores two persistent extension values *DEX_extStart* and *DEX_extEnd* so the dialog remembers your last used distances between runs. • DCL creation: Dynamically writes a temporary DCL file that defines the Double Extend dialog with two edit boxes (Extend Start and Extend End) and buttons for Apply, Undo, OK and Cancel. • Dialog behavior: Each time the dialog is shown it pre fills the edit boxes from the global values and updates those globals when you press Apply or OK, converting strings to distances. • Return codes: The dialog function returns a code that distinguishes between OK, Cancel, Apply and Undo so the main routine can decide what to do without re selecting geometry. • Selection and group: The command first gathers a selection set of eligible entities, then starts an overall UNDO group so the entire session can be undone as one operation if desired. • Apply loop: When you press Apply the routine places an UNDO mark, calls the geometry engine to extend all selected entities by the current start and end values, increments an internal apply counter and regenerates the drawing. • Undo button: Pressing Undo triggers an UNDO back to the last mark, rolling back the most recent Apply, decrementing the apply counter and updating the drawing again. • OK semantics: If you have never used Apply or Undo, pressing OK performs one single extension using the current values and then exits; if you have already applied or undone changes, OK simply accepts the current state without further modification. • Cancel semantics: If you press Cancel or close the dialog without confirming, the routine repeats UNDO back as many times as there were Apply operations, fully restoring the pre command state and then ends the UNDO group. • End of session: After leaving the dialog loop the command always closes the UNDO group, making the final chosen state a single undo step from normal AutoCAD undo.