Regexp notes

regexp.txt

[^] -> any character that is not in the empty set of characters
.   -> any number of non-newline characters

(+, *, ?, and {}) -> Greedy
(+?, *?, ??, {}?) -> Nongreedy

\b -> word boundary
\w -> alpha numerical [A-Za-z0-9_]
\d -> number
\s -> single white space

flags
  g -> global (match all matches)
  i -> case intensitive
  
  ^ -> beginning of input
  $ -> end of input
  
  caution!
    ^   -> could be used as both beggining and not. For example /[^\w\s]/ it correponds 'not' in here, none of word and space
           http://eloquentjavascript.net/09_regexp.html#p_0Mx4Lf/w4/
    $&  -> means whole match when used as a second arg of replace method 
           http://eloquentjavascript.net/09_regexp.html#p_0Mx4Lf/w4/