Method doUndo

tools/xsbug/behaviors.js:109–120

(code)

		this.onSelected(code);
	}
	doUndo(code) {
		if (this.historyIndex == this.history.length)
			this.history.push(new CodeState(code));
		this.historyIndex--;
		var state = this.history[this.historyIndex];
		code.string = state.string;
		code.select(state.selectionOffset, state.selectionLength);
		this.insertionOffset = -1;
		this.onEdited(code);
		this.onSelected(code);
		this.onReveal(code);
	}
	filterKey(code, key) {
		if (!key) return null;
		var c = key.charCodeAt(0);