Examples from "Form Optional / Required" section of the form reference: form.mustvalue - a schema-required field is *displayed* as optional when form.mustvalue=false, still the value must be present to validate

Field Required *Standard required field that when HTML5 is enabled does not admit the empty string

Field Required Must Value False(Optional)Required field with form.mustvalue=false, is displayed and can be submitted empty (also when HTML5 is enabled) but does not validate if there is no input