As Cap blocks are designed to stop a script, their bottom is smooth; that way no blocks can be placed under them. Other than that, their shape is identical to the Stack block - they still have the notch on the top, so you can place the block below others.
The need to stop a script (or all scripts) can be found in several occasions. Some include:
- Disabling a script that will continuously set a variable
- Once the game is completed, all scripts must stop
- 'Killing' a sprite
An example follows:
Note how the Cap block (Stop Script) is used - if the selected letter is "z", the script stops.