code: private void addContraintExamples() {
  		add(new WHeading(HeadingLevel.H2, "Date fields with input constraints"));
  		WFieldLayout layout = new WFieldLayout();
  		layout.setLabelWidth(33);
  		add(layout);
  
  		/* mandatory */
  		WDateField constrainedDateField = new WDateField();
  		constrainedDateField.setMandatory(true);
  		layout.addField("Mandatory date field", constrainedDateField);
  
  		/* min date */
  		constrainedDateField = new WDateField();
  		constrainedDateField.setMinDate(new Date());
  		layout.addField("Minimum date today", constrainedDateField);
  
  		/* max date */
  		constrainedDateField = new WDateField();
  		constrainedDateField.setMaxDate(new Date());
  		layout.addField("Maximum date today", constrainedDateField);
  
  		/* auto complete */
  		constrainedDateField = new WDateField();
  		constrainedDateField.setBirthdayAutocomplete();
  		layout.addField("With autocomplete hint", constrainedDateField);
  		constrainedDateField = new WDateField();
  		constrainedDateField.setAutocompleteOff();
  		layout.addField("With autocomplete off", constrainedDateField);
  	}
docs: Add constraint example.