RE precedence

Table 8-1. Regular expression precedence
↓  Regular expression feature              Example
↓  Parentheses                            (grouping or memory) (...), (?:...),    (?...)
↓  Quantifiers                             a* a+ a? a{n,m}
↓  Anchors and sequence                    abc ^a a$
↓ Alternation                             a|b|c
↓  Atoms                                  a [abc] \d \1