acf_form_head()

Description
Used to process, validate and save the submitted form data created by the acf_form() function. It will also enqueue all ACF related scripts and styles for the form to display correctly.
This function must be placed before any HTML has been output, preferably above the 
get_header() function of your theme file.
Parameters
acf_form_head();
Example
This example demonstrates a basic 
acf_form() to edit the current post being viewed.
<?php acf_form_head(); ?>
<?php get_header(); ?>
    <div id="primary" class="content-area">
        <div id="content" class="site-content" role="main">
            <?php acf_form(); ?>
        </div>
    </div>
<?php get_sidebar(); ?>
<?php get_footer(); ?>
Actions & Filters
The following actions and filters are provided to customize the submission process.
acf/pre_submit_form
This filter is run after a form has been submit, and before any data has been saved.
Use this filter to modify the 
$form array before 
$_POST data is saved.
add_filter('acf/pre_submit_form', 'my_acf_pre_submit_form', 10, 1);
function my_acf_pre_submit_form( $form ) {
    // Create post using $form['new_post'].
    // Modify $form['redirect'].
    return $form;
}
acf/pre_save_post
This filter is run after the acf/pre_submit_form filter, and before any data has been saved.
Use this filter to modify the 
$post_id value used to save the 
$_POST data.
add_filter('acf/pre_save_post', 'my_acf_pre_save_post', 10, 2);
function my_acf_pre_save_post( $post_id, $form ) {
    // Create post using $form and update $post_id.
    return $post_id;
}
acf/save_post
This action runs when ACF saves the 
$_POST data.
For more information, please refer to the acf/save_post guide.
add_action('acf/save_post', 'my_acf_save_post', 20);
function my_acf_save_post( $post_id ) {
    // Get new value.
    $value = get_field('my_field', $post_id);
    // Do something.
}
acf/submit_form
This action runs after the 
$_POST data has been saved.
Use this action to perform custom logic before the return setting is used to redirect the browser.
add_action('acf/submit_form', 'my_acf_submit_form', 10, 2);
function my_acf_submit_form( $form, $post_id ) {
    // Get new value.
    $value = get_field('my_field', $post_id);
    // Redirect.
    wp_redirect( 'http://www.website.com/' . $value );
    exit;
}
Changelog
acf/pre_submit_form added in version 5.5.10
acf/submit_form added in version 5.5.10
acf/pre_save_post added in version 4.1.6