Press F11 when cursor is in the editor to toggle full
screen editing. ESC can also be used to exit full
screen editing.
Press CTRL-Q when cursor is at start of active line to toggle
fold/unfold.
Press CTRL-SPACE for very simple code completion.
Search and replace seem to be pretty bad.
Press CTRL-F when cursor is in the editor to Search. Find Next with CTRL-G. Find Previous with SHIFT-CTRL-G.
Press SHIFT-CTRL-F when cursor is in the editor to Replace. Press SHIFT-CTRL-R to Replace All.
This editor uses CodeMirror 3,
a Javascript based MIT licensed code editor.