post_class filter code example

Example 1: what is post_class()

/*  A simple way to add multiple classes to the post_class defaults, is to just write them as a string argument:  */

<div <?php post_class( 'class1 class2 class3' ); ?>>

Example 2: what is post_class()

/* we see in php code  */
<div id="post-<?php the_ID(); ?>" <?php post_class( 'class-name' ); ?>>

/*  we see in html code like this   */
<div id="post-4564" class="class-name post-4564 post type-post status-publish format-standard hentry category-news">