(Composition and Layer windows)
Result
Windows
Macintosh
Reset oval or rectangle mask to fill window
Double-click rectangular or oval mask tool
Scale around center point in Free Transform mode
Ctrl-drag
Command-drag
Select all points in a mask
Alt-click mask
Option-click mask
Free transform mask
Ctrl + T, or double-click mask
Command + T, or double-click mask
Exit free transform mask
Enter
Return
Set an initial keyframe on a selected mask
Shift + Alt + M
Shift + Option + M