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$v = Boar::create()
$v->field("name")->isRequired()->alphabetic()->maxLen(50)
$v->fields(["email", "address"])->areRequired()->maxLen(50)

$res = $v->validate($post_values)

if($res->hasErrors())
{
    echo json_encode($res->errors);    
}

Customizing the error message

$v->field("name")->maxLength(10)->withMessage("name should be shorter than {{max_length}}");

The message string is a template. {{field}} is replaced with the name of the field. For example, "{{field}} is required." when used with field address becomes "address is required". The message template can contain values from the specific validation as well. For example, max_length for MaxLength validation and min_length for MinLength validation.

All validations should be explicitly declared

$v->field("name")->maxLength(10)->alphabetic();

$res = $v->validate([]); //No Error. 

if name is a required field, should call isRequired() explicitly

$v->field("name")->isRequired()->maxLength(10)->alphabetic();

$res = $v->validate([]); //Error. 

Similarly,

$v->field("weight")->min(100);

$res = $v->validate(["weight"=>"not a number"]); //No Error. 

minimum validation will not validate for the data type. If the value is not number, it will silently ignore.

$v->field("weight")->isNumber()->min(100);

$res = $v->validate(["weight"=>"not a number"]); //Error. 

Keeping the granularity of the validation helps in predictable behavior and reduces ambiguity.