reference

var (
	// AnchoredTagRegexp matches valid tag names, anchored at the start and
	// end of the matched string.
	AnchoredTagRegexp = regexp.MustCompile(anchored(tag))

	// AnchoredDigestRegexp matches valid digests, anchored at the start and
	// end of the matched string.
	AnchoredDigestRegexp = regexp.MustCompile(anchored(digestPat))
)