C-c C-r for Ocaml toplevel and setting a region under Emacs

I have seen somewhere the description of C-c C-r is "evaluate the whole selected region" or tuareg-eval-region. But when I try it under Emacs, it seems that after setting a region, and placing the cursor several commands after the end of the region, pressing C-c C-r evaluates until the position of the cursor.

So could anyone te开发者_C百科ll me if C-c C-r evaluates "until the cursor" or a region that we set before?

By the way, I am not sure I have set the region correctly. One way is to use SHIFT + direction arrow; another way is to use CTRL + space, but i do not know the difference between Mark set, Mark activated and Mark cleared. Could anyone tell me the right way to select a region?

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In Emacs parlance, the region is the area between the mark and point (i.e., the cursor). Thus, when you move the cursor, you move one boundary of the region while the other remains wherever the current mark is.

C-SPC is the traditional way of setting the mark. Nowadays, Shift + cursor keys should work as well. See the relevant section of the Emacs manual for details on how regions work.