1. A method comprising: outputting, by a computing device and for display at a presence-sensitive display, a graphical user interface associated with an application executing at the computing device, the graphical user interface comprising an input field and a graphical keyboard, the graphical keyboard comprising a group of keys, wherein each key in the group of keys is associated with a respective, different region of the presence-sensitive display; receiving, at the computing device, an indication of a gesture to select a sequence of keys that are each included in the group of keys of the graphical keyboard; determining, by the computing device, that the selected sequence of keys corresponds to a character string that is identifiable by a format source, wherein the format source is associated with a syntax, the format source and the syntax being determined based on syntax information associated with the input field; determining, by the computing device and based at least in part on the syntax, that at least one separator character is associated with the character string, wherein the gesture does not indicate a key associated with the at least one separator character, and wherein the syntax comprises a set of rules that define one or more combinations of symbols or characters that are structurally valid in a given context defined as the input field; and in response to determining that the at least one separator character is associated with the character string for the given context, outputting, by the computing device, for display within the input field, the character string and the at least one separator character between at least two characters of the character string.