Difference between input range and forward range

[via Digitalmars-d]

I think that we should document it somewhere in order to prevent 
future mistakes in algorithms that copies and +save+s ranges. I 
think that lots of algorithms could rely on that initializing new 
range or copying via opAssign will create independent range, but 
not really all do it. So we must somehow pay attention to it, 
write some article on working with ranges, because there are a 
lot of aspects that not clear for me and other. This could make 
library much better.