Regular expression for survival

0. A truth for the regular expression
  Regular expression is used to matching pattern in a line. (Not laid on multiple lines.)

1. The Structure of a regular expression
  1) Anchors
    (1) ^ : begin of a line
    (2) $ : end of a line
    (3) \< ... \> : word level matching.

  2) Character sets
    (1) . : any char except the EOL char.
    (2) [...] : any char in brackets.
      a. range : [a-z], [0-9], [A-Za-z0-9_]
      b. order : "^T[a-z][aeiou] " : Tha, The, Thi, ...
    (3) [^...] : negate pattern. except chars in brackets.
    (4) \( ... \) : remembered pattern. use it with "\1 ~ \9"

  3) Modifiers : follows a character set. if not, not a modifier.
    (1) * : 0 or more copies
    (2) {a,b} : # of copies between a and b.