You should not be permitted to write production code if you do not have an journeyman licence in regular expressions or floating point math. —Rob Pike
. single character
\ escape
? optional character
* zero or more of previous
+ one ore more
| or on the word level
[] or for specific characters
^ not
\d digit
\s whitespace (tabs, carriage returns, null)
\b word boundary
\d{4} equiv \d\d\d\d
parenthesis and ? makes the stuff in parens optional
same for + and *
\w{n} n letter words
\w{n,k} n or k letter words
?*+ are "quantifiers"