fires when newly loaded/added/edited data fail to pass validation
| id | number|string | the ID of the data item that is being validated | 
| obj | object | the data item object | 
| details | object | the validation result for data keys under validation | 
webix.ui({
    view:"datatable",
    rules:{
        title:webix.rules.isNotEmpty,
        rating:webix.rules.isNumber
    },
    on:{
        onValidationError:function(id, obj, details){
            var index = this.getIndexById(id)+1;
            webix.message({ type:"error", text:"Empty title for row "+index });
        }
     }
});
The last parameter, details, contains invalid markers for each data key that has been validated and looks like:
{
    title:true,  // hasn't passed validation
    rating:false // has passed validation
}