WordPress custom posts navigation function

wp_custom_posts_navigation

<?php
// Adapted from Underscores' posts navigation function
// Uses Bootstrap classes

// In a default query:
// custom_posts_navigation();
 
// In a custom query:
// custom_posts_navigation($my_custom_query);
 
function custom_posts_navigation($custom_query = null) {
    $max = is_null($custom_query) ? $GLOBALS['wp_query']->max_num_pages : $custom_query->max_num_pages;
 
    if ( $max < 2 ) {
        return;
    }
    ?>
    <nav class="navigation posts-navigation" role="navigation">
        <h2 class="screen-reader-text">Posts navigation</h2>
        <ul class="nav-links pager">
 
            <?php if ( get_next_posts_link('', $max) ) : ?>
            <li class="previous"><?php next_posts_link('Older posts', $max); ?></li>
            <?php endif; ?>
 
            <?php if ( get_previous_posts_link() ) : ?>
            <li class="next"><?php previous_posts_link('Newer posts'); ?></li>
            <?php endif; ?>
 
        </ul><!-- .nav-links -->
    </nav><!-- .navigation -->
    <?php
}