AngleSharp by Florian Rappl

<PackageReference Include="AngleSharp" Version="0.8.9" />

.NET API 1,181,184 bytes

 IValidation

public interface IValidation
Implemented by elements that can be validated.
string ValidationMessage { get; }

Gets the current validation message.

IValidityState Validity { get; }

Gets the current validation state of the current element.

bool WillValidate { get; }

Gets a value if the current element validates.

bool CheckValidity()

Checks the validity of the current element.

void SetCustomValidity(string error)

Sets a custom validation error. If this is not the empty string, then the element is suffering from a custom validation error.