API for specifying display of complication on an electronic watch

Systems, methods, and devices can efficiently manage the displaying of text on a screen of a computing device. For example, a client application can provide a data object for a particular style window on the screen. The data object can include a data item, comprising text data, one or more units specifying one or more portions of the text data to be displayed in the style window, and an identifier corresponding to a particular display function to be used in displaying the text data. The display function can be invoked to determine a potential text string to display based on the text data, the one or more units, and one or more rules corresponding to the particular display function. Additional text strings can be generated to obtain a text string that is shorter than or equal to a maximum length for the data item.