1. A method, comprising: at an electronic device having a display and a touch-sensitive surface: displaying at least a portion of an electronic document that includes text that has a reading direction on the display; detecting a gesture on the touch-sensitive surface, wherein the gesture includes movement in a first direction on the touch-sensitive surface that corresponds to a second direction on the display; and in response to detecting the gesture: in accordance with a determination that the second direction on the display includes a directional component that is opposite to the reading direction, performing a navigation operation; and in accordance with a determination that the second direction on the display includes a directional component in the reading direction and that the gesture meets predefined criteria, performing an annotation operation.