`a+`,
	`a?`,
	`a|b`,
	`a*|b*`,
	`(a*|b)(c*|d)`,
	`[a-z]`,
	`[a-abc-c\-\]\[]`,
	`[a-z]+`,
	`[abc]`,
	`[^1234]`,
	`[^\n]`,
	`\!\\`,
}

type stringError struct {
	re  string
	err string
}

var badRe = []stringError{
	{`*`, "missing argument to repetition operator: `*`"},
	{`+`, "missing argument to repetition operator: `+`"},
	{`?`, "missing argument to repetition operator: `?`"},