| ^              REGEX METACHARS            REGEX MODIFIERS
 &&               ^     string begin         /i case insens.
 ||               $     str. end (before \n) /m line based ^$
 .. ...           +     one or more          /s . includes \n
 ?:               *     any amount           /x ign. wh.space
 = += -= *= etc.  ?     zero or one          /g global</b>
 , =>             ()    capture
 list ops         (?:)  no capture       REGEX CHARCLASSES
 not              []    character class  .  == [^\n]
 and              |     alternation      \s == [\x20\f\t\r\n]
 or xor           {1,2} amount           \w == [A-Za-z0-9_]
                  \b    word boundary    \d == [0-9] 
                  \z    string end       \S, \W and \D negate