A set of XML-based markers includes an event marker indicating an event, a condition marker indicating a state of a first media object, and an action marker indicating a second media object, an attribute of the second media object, and a value of the attribute. The markers represent a function to assign the value to the attribute of the second media object if the event is detected and if the first media object possesses the indicated state. A set of XML-based markers representing media object elements. Each marker includes a test-element attribute for indicating a particular media object element, a test-attribute attribute for indicating an attribute of the particular element, and a test-value attribute for indicating a test value to compare with a value of the specified attribute.