How to open the last page of levels

Guide on how to open the "door" to the last page of levels.

Open the DOOR with a KEY

To open the last page of levels, the "door" has to be unlocked with a "key".

Create a key symbol by combining K + E + Y
Create a door symbol by combining D + O + O + R

The level you are in will automatically change to a key symbol and a door symbol. Complete the level to unlock the last page.

An example built below:

[cram]

How do you get into this level? I get to the door and can't click on anything.

[Melissanoma]

You can also make the actual key and door symbols. key is O + (upside down F), door is (upside down U) + _ + O