RegEx
^ Start of the line $ End of the line s Whitespace S Not whitespace ?= Lookahead ?! Negative lookahead ?<= Lookbehind (usually has to be constant length) ?!= Negative lookbehind ?
? 0 or 1 * 0 or more + 1 or more {3} Exactly 3 {3,} 3 or more {7,9} Between 7 and 9, inclusive