What does:% S do in vim?

Question

As I tried to globally replace FOO with BAR in vim buffer, I accidentally typed

:%S/FOO/BAR/ 

Note the uppercase S instead of the more appropriate S

Of course, this will not replace my FOO. This is clear. However, vim split the window into two windows, both with the same buffer.

Unfortunately, I could not find :help in this behavior. So, can someone explain what uppercase should do :%S and where can I find help?

Answer 1

 :h :S 

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 :[N]Sexplore[!] [dir]... Split&Explore current file directory *:Sexplore*