Shortcuts
Hold Ctrl / Command:
Move the cursor to any of the four edges, then drag to skew the element.
Move the cursor to a control point, then drag to rotate the element.
Hold Alt: center scaling / skewing (Alt + Shift can be combined).
Hold Shift: multi-select / fixed-ratio scaling / fixed-direction movement / rotate around diagonal center.
Customization
Shortcuts can be customized by listening to keyboard events and dynamically modifying the editor configuration.