code: func isImageIDPrefix(imageID, possiblePrefix string) bool {
  	if strings.HasPrefix(imageID, possiblePrefix) {
  		return true
  	}
  
  	if i := strings.IndexRune(imageID, ':'); i >= 0 {
  		return strings.HasPrefix(imageID[i+1:], possiblePrefix)
  	}
  
  	return false
  }
docs: // isImageIDPrefix returns whether the given possiblePrefix is a prefix of the
  // given imageID.