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Browse with Left and Right arrow. Enter or Down arrow for selecting sub-level. Escape or Up arrow for back to super-level.
Space for toggling between showing these instructions and showing picture.
TIP: For small pictures, use Zoom functionality in browser (CTRL + / CTRL - in Chrome on a PC). (Zoom on a PC will not affect big pictures, but you can use pinch gestures)
TIP: Use full screen view (F11 in Chrome on a PC)