$validator = new Validator();

// Syntax to evaluate whether correct.
$validator->addEvaluation(new SyntaxEvaluation());
$validator->addEvaluation(new RequiredEvaluation(['test']));
$xml = '<?xml version="1.0" encoding="UTF-8"?><test></test>';

if ($validator->validate($xml)) {
  // success
} else {
  // fail
  $errors = $validator->errors();
}

// success required

$validator = new Validator();

// xml data
$xml = '...'; 

// required columns.
$columns = ['ok'];

// add required evaluation.
$validator->addEvaluation(new RequiredEvaluation($columns));

// true
$validator->validate($xml)



// success required(nest data)

$validator = new Validator();

// xml data
$xml = '...'; 

// required columns.
$columns = ['nest.ok'];

// add required evaluation.
$validator->addEvaluation(new RequiredEvaluation($columns));

// true
$validator->validate($xml)


//fail required
$validator = new Validator();

// xml data
$xml = '...'; 

// required columns.
$columns = ['ng'];

// add required evaluation.
$validator->addEvaluation(new RequiredEvaluation($columns));

// false
$validator->validate($xml)


//fail required(nest data)
$validator = new Validator();

// xml data
$xml = '...'; 

// required columns.
$columns = ['ng'];

// add required evaluation.
$validator->addEvaluation(new RequiredEvaluation($columns));

// false
$validator->validate($xml)