关于Control characters的疑问？

Control characters can be generated using ?\C-x and ?\c-x
(the control version of x is x & 0x9f).
Metacharacters (x | 0x80) can be generated using ?\M-x.
The combination of meta and control is generated using and ?\M-\C-x.
You can get the integer value of a backslash character using the sequence ?\\.

?a     => 97 # ASCII character
?\n    => 10 # code for a newline (0x0a)
?\C-a   => 1 # control a = ?A & 0x9f = 0x01
?\M-a   => 225 # meta sets bit 7
?\M-\C-a => 129 # meta and control a
?\C-?   => 127 # delete character

上面的一段英文，请解释一下，还有关于Control characters的知识点？