1. A method comprising: obtaining a selector string and information that represents one or more actions associated with the selector string; wherein the selector string represents one of (a) a query only on event targets that is satisfied by any event target of a particular type specified by the selector string or (b) a query only on event targets that is satisfied by any event target having an attribute with a particular name specified by the selector string; in response to obtaining an event, obtaining an event target that is a subject of the event; in response to determining that the event target matches the selector string, using the information to cause the one or more actions associated with the selector string; wherein determining that the event target matches the selector string includes performing one of (a) determining a type of the event target and determining that the type of the event target is the same as the particular type specified by the selector string or (b) determining that the event target has an attribute with the particular name specified by the selector string; wherein the method is performed by a computing device.