1. A system comprising: one or more processors; and one or more computer-readable storage media storing computer-executable instructions that, responsive to execution by the one or more processors, cause the system to perform operations including: detecting a pen in proximity to an input surface of a display device on which primary content is displayed; ascertaining a current ink mode from multiple different ink modes for the system responsive to said detecting, the different ink modes including a permanent ink mode in which ink applied becomes part of the primary content and a transient ink mode in which ink applied to the primary content is applied to a transient ink layer separate from the primary content and does not become part of the primary content, and the current ink mode corresponding to the transient ink mode; causing a visual affordance identifying the transient ink mode to be displayed on the display device responsive to said ascertaining; processing ink content applied to the primary content according to the transient ink mode, including: detecting that the pen is removed from proximity to the input surface; initiating a timer responsive to said detecting; propagating the ink content to the transient ink layer that is retrievable separate from the primary content; and removing the ink content from being displayed on the document responsive to expiry of the timer, the visual affordance being selectable to cause the ink content to be retrieved from the transient ink layer and displayed along with the primary content.
1. A system comprising: one or more processors; and one or more computer-readable storage media storing computer-executable instructions that, responsive to execution by the one or more processors, cause the system to perform operations including: detecting a pen in proximity to an input surface of a display device on which primary content is displayed; ascertaining a current ink mode from multiple different ink modes for the system responsive to said detecting, the different ink modes including a permanent ink mode in which ink applied becomes part of the primary content and a transient ink mode in which ink applied to the primary content is applied to a transient ink layer separate from the primary content and does not become part of the primary content, and the current ink mode corresponding to the transient ink mode; causing a visual affordance identifying the transient ink mode to be displayed on the display device responsive to said ascertaining; processing ink content applied to the primary content according to the transient ink mode, including: detecting that the pen is removed from proximity to the input surface; initiating a timer responsive to said detecting; propagating the ink content to the transient ink layer that is retrievable separate from the primary content; and removing the ink content from being displayed on the document responsive to expiry of the timer, the visual affordance being selectable to cause the ink content to be retrieved from the transient ink layer and displayed along with the primary content. 7. The system as described in claim 1 , wherein said processing comprises: receiving user input to retrieve ink content from the transient ink layer; and causing the transient ink layer to be retrieved such that the ink content is at least temporarily displayed with the primary content.