\class{FancyURLopener} class and use it to perform their requested

actions. To override this functionality, programmers can create a

subclass of \class{URLopener} or \class{FancyURLopener}, then assign

\code{urllib._urlopener} variable before calling the desired function.

For example, applications may want to specify a different

\mailheader{User-Agent} header than \class{URLopener} defines. This