How To Create a custom Pseudo Class

using System.Collections.Generic;
using SoyWar.UIToolkit;
using SoyWar.UIToolkit.PseudoClasses;
using UnityEngine;
using UnityEngine.UIElements;

public class CustomPseudoClass : PseudoClass
{
    [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.AfterAssembliesLoaded)]
    private static void Init()
    {
        // Adds to the list of usable pseudo-classes, which can be called by name in the Selector Parser and Selector Builder.
        PseudoClass.Add<CustomPseudoClass>("custom");
    }

    // Checks if the VisualElement is valid according to the rules of this pseudo-class
    public override bool Check(ICollection<VisualElement> roots, VisualElement visualElement, UIToolkitComponent.TypeSearch searchFrom)
    {
        // Example: The VisualElement is only valid if it is a TextField and if it contains the same content as the "Value" variable.
        return visualElement is TextField textField && textField.value == Value;
    }

    // Add Event to check validity though the pseudo class manipulator.
    protected override void AddManipulatorCallback(PseudoClassManipulator manipulator)
    {
        // Example: Checks the validity of the VisualElement each time the KeyUpEvent is called
        manipulator.AddEventCallback<KeyUpEvent>(() =>
        {
            // Updates the validity of the VisualElement through the rules of this pseudo class
            manipulator.CheckUpdate();
            
            // Equivalent to
            manipulator.Check = Check(manipulator);
            
            // Or
            manipulator.Check = Check(manipulator.Roots, manipulator.target, manipulator.SearchFrom);
        });
    }


    // Checks the validity of the pseudo-class when creating the selector
    protected override bool Validate()
    {
        //Example: The pseudo-class is only valid if it has a value
        return Value != null;
    }
}