code: @Override
  	public void checkSubType(final String subType) {
  		validateLength(subType,"Subtype");
  		validateFirstChar(subType,"subtype");
  		validateOtherChars(subType,"subtype");
  	}
docs: Checks the given {@code subtype} for illegal characters, as defined in RFC
  6838, section 4.2. NOTE: '*' is accepted as a valid subtype.
  
  @param subType
  the string to validate
  @throws IllegalArgumentException
  in case of illegal characters
  @see <a href="https://tools.ietf.org/html/rfc6838#section-4.2">Media Type
  Specifications and Registration Procedures, Section 4.2</a>