newsupernova/app/code/Magefan/Blog/view/adminhtml/layout/blog_post_relatedposts.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © 2015 Ihor Vansach (ihor@magefan.com). All rights reserved.
 * See LICENSE.txt for license details (http://opensource.org/licenses/osl-3.0.php).
 *
 * Glory to Ukraine! Glory to the heroes!
 */
-->
<layout xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/layout_generic.xsd">
    <container name="root" label="Root">
        <block class="Magefan\Blog\Block\Adminhtml\Post\Edit\Tab\RelatedPosts" name="blog.post.edit.tab.relatedposts"/>
        <block class="Magento\Backend\Block\Widget\Grid\Serializer" name="relatedposts_grid_serializer">
		    <arguments>
		    	<argument name="input_names" xsi:type="string">position</argument>
		        <argument name="grid_block" xsi:type="string">blog.post.edit.tab.relatedposts</argument>
		        <argument name="callback" xsi:type="string">getSelectedRelatedPosts</argument>
		        <argument name="input_element_name" xsi:type="string">links[relatedposts]</argument>
		        <argument name="reload_param_name" xsi:type="string">posts_related</argument>
		    </arguments>
		</block>
    </container>
</layout>