14. A non-transitory storage device, comprising: program instructions readable by a logic device, wherein the program instructions are executable by the logic device to cause a computing system to perform operations comprising: receiving data specifying a user input to select a portion of content of a rendered document, the selected document portion containing text; determining an encoded representation of text contained by the selected document portion, wherein determining the encoded representation of text contained by the selected document portion comprises determining a sequence of offsets that represent the text, and wherein each offset represents a number of character positions separating recurring instance of each letter within the text of the selected document portion; searching for the encoded representation of text within a corpus of electronic documents to identify (1) an electronic document contained in a corpus of electronic documents, the identified electronic document containing the selected document portion, and (2) a position within the identified electronic document at which the selected document portion occurs; and providing, for presentation on a display device, a menu of selectable user actions associated with the identified position in the identified electronic document, wherein at least one of the selectable user actions was associated with the identified position before the receipt of the data specifying the user input.
14. A non-transitory storage device, comprising: program instructions readable by a logic device, wherein the program instructions are executable by the logic device to cause a computing system to perform operations comprising: receiving data specifying a user input to select a portion of content of a rendered document, the selected document portion containing text; determining an encoded representation of text contained by the selected document portion, wherein determining the encoded representation of text contained by the selected document portion comprises determining a sequence of offsets that represent the text, and wherein each offset represents a number of character positions separating recurring instance of each letter within the text of the selected document portion; searching for the encoded representation of text within a corpus of electronic documents to identify (1) an electronic document contained in a corpus of electronic documents, the identified electronic document containing the selected document portion, and (2) a position within the identified electronic document at which the selected document portion occurs; and providing, for presentation on a display device, a menu of selectable user actions associated with the identified position in the identified electronic document, wherein at least one of the selectable user actions was associated with the identified position before the receipt of the data specifying the user input. 15. The non-transitory storage device of claim 14 , wherein the program instructions are further executable by the logic device to perform steps comprising: accessing a markup layer that relates to the identified electronic document; and identifying actions defined by the markup layer for the identified position in the identified electronic document, wherein the identified actions are presented within the menu of selectable user inputs.