src/vs/editor/browser/controller/mouseHandler.ts/MouseHandler/getTargetAtClientPoint
class MouseHandler:	public getTargetAtClientPoint(clientX: number, clientY: number): IMouseTarget | null {
		const clientPos = new ClientCoordinates(clientX, clientY);
		const pos = clientPos.toPageCoordinates();
		const editorPos = createEditorPagePosition(this.viewHelper.viewDomNode);

		if (pos.y < editorPos.y || pos.y > editorPos.y + editorPos.height || pos.x < editorPos.x || pos.x > editorPos.x + editorPos.width) {
			return null;
		}

		const relativePos = createCoordinatesRelativeToEditor(this.viewHelper.viewDomNode, editorPos, pos);
		return this.mouseTargetFactory.createMouseTarget(this.viewHelper.getLastRenderData(), editorPos, pos, relativePos, null);
	}