Pieces are used to concatenate one or more REs, or to specify how often a precedent piece must be repeated
| (r) | the RE r itself |
| rs | the RE r followed by the RE s |
| r|s | the RE r OR the RE s |
| r* | the RE r zero or more times |
| r+ | the RE r one or more time |
| r? | the RE r zero or one time |
| r{2,6} | the RE r anywhere from two to six times |
| r{2,} | the RE r two or more times |
| r{,6} | the RE r up to six times |
| r{4} | the RE r exactly for times |