The cap device is a two-terminal capacitor. Typically, a value property is added to specify capacitance. Alternatively, a model property can be added to specify a capacitor model. If a model property is assigned, then a param property can be used to supply the geometric parameters. In either case, the param property can be used to provide initial conditions.
The `+ ' symbol in the representation accesses a branch property that returns a hypertext expression consisting of the capacitance value times the time-derivative of the voltage across the capacitor, yielding the capacitor current.