The function copyfmt() copies all format information (see Section 15.7.1, page 779), including
the arrays accessed with iword() and pword(). This may pose a problem for the objects stored
with a stream using pword(). For example, if a value is the address of an object, the address is
copied instead of the object. If you copy only the address, it may happen that if the format of one
stream is changed, the format of other streams would be affected. In addition, it may be desirable
that an object associated with a stream using pword() be destroyed when the stream is destroyed.
So, a deep copy rather than a shallow copy may be necessary for such an object.