public static boolean isValidTag(String tag) {
    return tag.matches(TAG_REGEX);
  }
Returns {@code true} if {@code tag} is a valid tag string. For example, a valid tag could be
{@code v120.5-release}.

@param tag the tag to check
@return {@code true} if is a valid tag; {@code false} otherwise
jib-core/src/main/java/com/google/cloud/tools/jib/api/ImageReference.java