Undiscoverable Features

When dragging a selection of files to a destination on the same volume, the files will be moved by default. Hold down △ before letting go of the mouse button to force a copy instead. Files dragged to a different volume will always be copied.
Hold down △ when launching DESKTOP.SYSTEM to prevent DeskTop from being copied to a RAM card. (A tip is now shown for this while copying.)
Desk Accessory files with high bit set in the aux type field ($8640) will not appear in the Apple menu.
You can't run a Binary file by double-clicking, but you can run it with the △O shortcut or holding down △ or ▲ while selecting File > Open.
The Sort Directory desk accessory has two modes:
- If any files are selected, these are moved to the start of the directory listing, in selection order; other files appear after, order unchanged.
- If no files are selected, all files are sorted by type: DIR, then TXT, then SYS, then others in descending (numeric) order.
Hold down △ or ▲ when opening a folder using double-click or File > Open to close the parent folder.
- Note: Does not work with the △O shortcut.
The Control Panel desk accessory writes settings back to the DESKTOP2 file when it is closed. If it is not present, or is locked, the settings will not be saved for the next session.

File Types

Binary files (type $06) with aux type $2000 or $4000 are treated as Graphics files (HR/DHR)
Binary files (type $06) with aux type $5800 are treated as Graphics files (Minipix/Print Shop)
Desk Accessory files have type $F1, and auxtype $640 or $8640

The Calculator desk accessory has a tiny monogram resembling "JB" drawn in the title bar - possibly "J. Bernard" thanked in the credits?
The string "Rien" appears in a couple of places in the code. Is this a name?
In the "This Apple" desk accessory, type E to see what other Apple models look like.