Merge tag class with callback

MergeTags.php

<?php if ( ! defined( 'ABSPATH' ) ) exit;

/**
 * Class NF_MergeTagExample_MergeTags
 */
final class NF_MergeTagExample_MergeTags extends NF_Abstracts_MergeTags
{
    protected $id = 'mergetag-example';

    public function __construct()
    {
        parent::__construct();

        $this->title = __( 'Merge Tag Example', 'ninja-forms-mergetag-example' );

        $this->merge_tags = NF_MergeTagExample()->config( 'MergeTags' );
    }

    /**
     * Example Tag Callback
     *
     * This is the call back method for our merge tag set in our config array.
     *
     * @return string
     */
    public function example_tag()
    {
        // Do stuff
        return __( 'Example Text', 'ninja-forms-mergetag-example' );
    }

}