The RootOf command can accept a root selector as an optional argument. Selectors are meant to specify a particular root of an equation or a subset of the roots. They can also be used for working with several (not necessarily specified) roots of the same polynomial. One of the types of selectors supported is a bounding box defined by two complex numbers a and b. The numbers should be given in the order of the lower-left corner of the box to the upper-right corner of the box (or left and right endpoints, in the case of a real interval), otherwise, an error will be raised. Moreover, if there is no root contained in the range, an error will be raised.
