Where to learn about "analog prototype filters"? Where to learn about "analog prototype filters"?

I've heard about them, but I'm unsure about what they really are and how they're constructed.
"Analog prototype" filters are well-known analog filters that have specific desirable properties. They include (but aren't limited to):


Butterworth filters: maximally-flat passband response
Chebyshev filters: sharper rolloff than Butterworth, equiripple in either the passband or stopband
Elliptic filters: even sharper rolloff, equiripple in passband and stopband
Bessel filters: maximally-flat group delay


These prototypes can be used to design digital filters that have approximately the same characteristics, for instance by using the bilinear transform.