case 'A':
					p.op(OpBeginText)
					t = t[2:]
					break BigSwitch
				case 'b':
					p.op(OpWordBoundary)
					t = t[2:]
					break BigSwitch
				case 'B':
					p.op(OpNoWordBoundary)
					t = t[2:]
					break BigSwitch
				case 'C':
					// any byte; not supported
					return nil, &Error{ErrInvalidEscape, t[:2]}
				case 'Q':
					// \Q ... \E: the ... is always literals