$: end of a string^: beginning of a string.: any character
Class/group of character:
[]: a class of characters, i.e, anything that is in the brackets[^]: complementary class, anything that is not in this class-: interval within a class|: logical OR(): substring
Quantification:
?: optional but if it appears, only 1 time. I.e, 0 to 1 occurence*: optional and if it appears, it can be any number of times. I.e, 0 to any number of occurence+: must appear any number of times. I.e, 1 to any number of occurence{x}: must appear exactly x times.{x,}: must appear at least x times.{x,y}: must appear between x to y times.
