Unity Editor script for filtering layers via keyboard

LayerMenu.cs

using UnityEditor;
using UnityEngine;

public static class LayerMenu
{
    /* PLACE IN EDITOR FOLDER.
     * Feel free to change hotkeys depending on your preference.
     * Modifier Keys % (ctrl on Windows, cmd on OS X), # (shift), & (alt), _ (no key modifiers) */

    #region Layer Visibility
    /// <summary> Only the selected layer will be visible in the editor. </summary>
    [MenuItem("Edit/Selection/Show Only Selected Layer _l", false)]
    static void LayersShowOnlySelected()
    {
        Transform selected = Selection.activeTransform;
        int layerNumber = selected.gameObject.layer;
        LayerMask layerNumberBinary = 1 << layerNumber; // This turns the layer number into the right binary number
        Tools.visibleLayers = layerNumberBinary; // This lets us set which layers are visible in the scene view.
        SceneView.RepaintAll();  // We need to repaint the scene
         }

    /// <summary> Make all layers visible in the editor. </summary>
    [MenuItem("Edit/Selection/Show All Layers _;", false)]
    static void LayersShowEverything()
    {
        Tools.visibleLayers = -1; // This lets us set which layers are visible in the scene view.
        SceneView.RepaintAll(); // We need to repaint the scene
    }

    /// <summary> Make the selected layer visible in the editor. </summary>
    [MenuItem("Edit/Selection/Show Layer _k", false)]
    static void LayersShowLayer()
    {
        Transform selected = Selection.activeTransform;
        int layerNumber = selected.gameObject.layer;
        LayerMask layerNumberBinary = 1 << layerNumber; // This turns the layer number into the right binary number
        Tools.visibleLayers = Tools.visibleLayers |= layerNumberBinary; // This lets us set which layers are visible in the scene view.
        SceneView.RepaintAll(); // We need to repaint the scene
         }

    /// <summary> Make the selected layer invisible in the editor. </summary>
    [MenuItem("Edit/Selection/Hide Layer _j", false)]
    static void LayersHideLayer()
    {
        Transform selected = Selection.activeTransform;
        int layerNumber = selected.gameObject.layer;
        LayerMask layerNumberBinary = 1 << layerNumber; // This turns the layer number into the right binary number
        LayerMask flippedVisibleLayers = ~Tools.visibleLayers;
        Tools.visibleLayers = ~(flippedVisibleLayers | layerNumberBinary); // This lets us set which layers are visible in the scene view.
        SceneView.RepaintAll(); // We need to repaint the scene
         }

    /// <summary> Copy layer of selected gameObject to all of its children. </summary>
    [MenuItem("Edit/Selection/Layer to Children _'", false)]
    static void LayerToChildren()
    {
        Transform selected = Selection.activeTransform;
        int layerNumber = selected.gameObject.layer;
        Transform[] children = selected.GetComponentsInChildren<Transform>(true);
        foreach (Transform item in children)
        {
            if (item.gameObject.layer == layerNumber)
                continue; // Skip like tags
            Undo.RecordObject(item.gameObject, "Layer To Children");
            item.gameObject.layer = layerNumber;
            EditorUtility.SetDirty(item.gameObject);
        }
         }

    #endregion

    #region Validation

    [MenuItem("Edit/Selection/Show Only Selected Layer _l", true)]
    static bool ValidateLayersShowOnlySelected()
    {
        return IsOneGameObjectSelected();
    }

    [MenuItem("Edit/Selection/Show Layer _k", true)]
    static bool ValidateLayersShowLayer()
    {
        return IsOneGameObjectSelected();
    }

    [MenuItem("Edit/Selection/Hide Layer _j", true)]
    static bool ValidateLayersHideLayer()
    {
        return IsOneGameObjectSelected();
    }

    [MenuItem("Edit/Selection/Layer to Children _'", true)]
    static bool ValidateLayerToChildren()
    {
        return IsOneGameObjectSelected();
    }

    /// <summary> Determines if is one game object selected. </summary> 
    /// <returns><c>true</c> if is one game object selected; otherwise, <c>false</c>.</returns>
    static bool IsOneGameObjectSelected()
    {
        return Selection.activeGameObject != null && Selection.transforms.Length == 1;
    }

    #endregion
}