Used to separate sub-patterns. See example

A, B	A followed by B
A | B	A or B
A & B	A interleave B — explained later

• parentheses used for grouping
• within a group, the content delimiters must all be the same
• e.g.

  { A, ( one | two | ( a & b & c ) ), B }

See example 06 rnc, xml