function unmap(keystroke, domain) {
        if (_isDomainApplicable(domain)) {
            var old_map = normal.mappings.find(KeyboardUtils.encodeKeystroke(keystroke));
            if (old_map) {
                normal.mappings.remove(KeyboardUtils.encodeKeystroke(keystroke));
            } else {
                for (var k in Mode.specialKeys) {
                    var idx = Mode.specialKeys[k].indexOf(keystroke);
                    if (idx !== -1) {
                        Mode.specialKeys[k].splice(idx, 1);
                    }
                }
            }
        }
    }
Unmap a key sequence in normal mode.

@param {string} keystroke a key sequence to be removed.
@param {regex} [domain=null] a Javascript regex pattern to identify the domains that this mapping will be removed.

@example
unmap("<<", /youtube.com/);