metaboxes.php

<?php
namespace PWCC;


/**
 * Register meta box(es).
 */
function wpdocs_register_meta_boxes() {
	add_meta_box( 'meta-box-id', __( 'My Meta Box', 'textdomain' ), __NAMESPACE__ . '\\wpdocs_my_display_callback', 'post' );
}
add_action( 'add_meta_boxes', __NAMESPACE__ . '\\wpdocs_register_meta_boxes' );

/**
 * Meta box display callback.
 *
 * @param WP_Post $post Current post object.
 */
function wpdocs_my_display_callback( $post ) {
	// Display code/markup goes here. Don't forget to include nonces!
	echo "<p>Yo</p>\n";
}

/**
 * Save meta box content.
 *
 * @param int $post_id Post ID
 */
function wpdocs_save_meta_box( $post_id ) {
	// Save logic goes here. Don't forget to include nonce checks!
}
add_action( 'save_post', __NAMESPACE__ . '\\wpdocs_save_meta_box' );