-----
    | User Username
    |--------------------------------------------------------------------------
    */

    'username' => array(
        'id' => 'username',
        'tag' => '{wp:user_username}',
        'label' => esc_html__( 'User Username', 'ninja_forms' ),
        'callback' => 'user_username'
    ),

    /*
    |--------------------------------------------------------------------------
    | User Email Address
    |--------------------------------------------------------------------------
    */

    'user_email' => array(
        'id' => 'user_email',
        'tag' => '{wp:user_email}',
        'label' => esc_html__( 'User Email', 'ninja_forms' ),
        'callback' => 'user_email'
    ),

    /*
    |--------------------------------------------------------------------------
    | User Website Address
    |--------------------------------------------------------------------------
    */

    'user_url' => array(
        'id' => 'user_url',
        'tag' => '{wp:user_url}',
        'label' => esc_html__( 'User URL', 'ninja_forms' ),
        'callback' => 'user_url'
    ),

    /*
     |--------------------------------------------------------------------------
     | Post Meta
     |--------------------------------------------------------------------------
     */

    'user_meta' => array(
        'id' => 'user_meta',
        'tag' => '{user_meta:YOUR_META_KEY}',
        'label' => esc_html__( 'User Meta', 'ninja_forms' ),
        'callback' => null
    ),

    /*
    |--------------------------------------------------------------------------
    | Site Title
    |--------------------------------------------------------------------------
    */

    'site_title' => array(
        'id' => 'site_title',
        'tag' => '{wp:site_title}',
        'label' => esc_html__( 'Site Title', 'ninja_forms' ),
        'callback' => 'site_title'
    ),

    /*
    |--------------------------------------------------------------------------
    | Site URL
    |--------------------------------------------------------------------------
    */

    'site_url' => array(
        'id' => 'site_url',
        'tag' => '{wp:site_url}',
        'label' => esc_html__( 'Site URL', 'ninja_forms' ),
        'callback' => 'site_url'
    ),

    /*
    |--------------------------------------------------------------------------
    | Admin Email Address
    |--------------------------------------------------------------------------
    */

    'admin_email' => array(
        'id' => 'admin_email',
        'tag' => '{wp:admin_email}',
        'label' => esc_html__( 'Admin Email', 'ninja_forms' ),
        'callback' => 'admin_email'
    ),

));