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.

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.