code: public static Map<String, Map<String, Map<String, Map<String, ?>>>> getCoreValidationConstraints() {
  		if (CORE_CONSTRAINTS.isEmpty()) {
  			for (Map.Entry<String, Class<? extends ParaObject>> e : ParaObjectUtils.getCoreClassesMap().entrySet()) {
  				String type = e.getKey();
  				List<Field> fieldlist = Utils.getAllDeclaredFields(e.getValue());
  				for (Field field : fieldlist) {
  					Annotation[] annos = field.getAnnotations();
  					if (annos.length > 1) {
  						Map<String, Map<String, ?>> constrMap = new HashMap<>();
  						for (Annotation anno : annos) {
  							if (isValidConstraintType(anno.annotationType())) {
  								Constraint c = fromAnnotation(anno);
  								if (c != null) {
  									constrMap.put(c.getName(), c.getPayload());
  								}
  							}
  						}
  						if (!constrMap.isEmpty()) {
  							if (!CORE_CONSTRAINTS.containsKey(type)) {
  								CORE_CONSTRAINTS.put(type, new HashMap<>());
  							}
  							CORE_CONSTRAINTS.get(type).put(field.getName(), constrMap);
  						}
  					}
  				}
  			}
  		}
  		return Collections.unmodifiableMap(CORE_CONSTRAINTS);
  	}
docs: Returns all validation constraints that are defined by Java annotation in the core classes.
  
  @return a map of all core types to all core annotated constraints. See JSR-303.