code: public static String getDataTypePattern(String datatypeKey)
      {
      	Datatype datatype = getDatatype(datatypeKey);
      	return datatype.getPattern();
      }
docs: Retrieves the pattern (regular expression) used by the identifiers within a data type.
  
  @param datatypeKey data type ID, name (or synonym), or URI (URL or URN)
  @return pattern of the data type
  
  @throws IllegalArgumentException when datatype not found