Allowing HTML within WordPress excerpt

Allowing HTML within WordPress excerpt is a very common request. Therefore, I am providing likely the most complete solution available on the Internet. The code is posted on stack exchange WordPress channel and is created by Pieter Goosen. The complete explanation with further examples can be found on the link provided.

function wpse_allowedtags() {
    // Add custom tags to this string
        return '<script>,<style>,<br>,<em>,<i>,<ul>,<ol>,<li>,<a>,<p>,<img>,<video>,<audio>'; 
    }

if ( ! function_exists( 'wpse_custom_wp_trim_excerpt' ) ) : 

    function wpse_custom_wp_trim_excerpt($wpse_excerpt) {
    $raw_excerpt = $wpse_excerpt;
        if ( '' == $wpse_excerpt ) {

            $wpse_excerpt = get_the_content('');
            $wpse_excerpt = strip_shortcodes( $wpse_excerpt );
            $wpse_excerpt = apply_filters('the_content', $wpse_excerpt);
            $wpse_excerpt = str_replace(']]>', ']]&gt;', $wpse_excerpt);
            $wpse_excerpt = strip_tags($wpse_excerpt, wpse_allowedtags()); /*IF you need to allow just certain tags. Delete if all tags are allowed */

            //Set the excerpt word count and only break after sentence is complete.
                $excerpt_word_count = 75;
                $excerpt_length = apply_filters('excerpt_length', $excerpt_word_count); 
                $tokens = array();
                $excerptOutput = '';
                $count = 0;

                // Divide the string into tokens; HTML tags, or words, followed by any whitespace
                preg_match_all('/(<[^>]+>|[^<>s]+)s*/u', $wpse_excerpt, $tokens);

                foreach ($tokens[0] as $token) { 

                    if ($count >= $excerpt_length && preg_match('/[,;?.!]s*$/uS', $token)) { 
                    // Limit reached, continue until , ; ? . or ! occur at the end
                        $excerptOutput .= trim($token);
                        break;
                    }

                    // Add words to complete sentence
                    $count++;

                    // Append what's left of the token
                    $excerptOutput .= $token;
                }

            $wpse_excerpt = trim(force_balance_tags($excerptOutput));

                $excerpt_end = ' <a href="'. esc_url( get_permalink() ) . '">' . '&nbsp;&raquo;&nbsp;' . sprintf(__( 'Read more about: %s &nbsp;&raquo;', 'wpse' ), get_the_title()) . '</a>'; 
                $excerpt_more = apply_filters('excerpt_more', ' ' . $excerpt_end); 

                //$pos = strrpos($wpse_excerpt, '</');
                //if ($pos !== false)
                // Inside last HTML tag
                //$wpse_excerpt = substr_replace($wpse_excerpt, $excerpt_end, $pos, 0); /* Add read more next to last word */
                //else
                // After the content
                $wpse_excerpt .= $excerpt_more; /*Add read more in new paragraph */

            return $wpse_excerpt;   

        }
        return apply_filters('wpse_custom_wp_trim_excerpt', $wpse_excerpt, $raw_excerpt);
    }

endif; 

remove_filter('get_the_excerpt', 'wp_trim_excerpt');
add_filter('get_the_excerpt', 'wpse_custom_wp_trim_excerpt');

function wpse_allowedtags() {

// Add custom tags to this string

return '<script>,<style>,<br>,<em>,<i>,<ul>,<ol>,<li>,<a>,<p>,<img>,<video>,<audio>';

}

if ( ! function_exists( 'wpse_custom_wp_trim_excerpt' ) ) :

function wpse_custom_wp_trim_excerpt($wpse_excerpt) {

$raw_excerpt = $wpse_excerpt;

if ( '' == $wpse_excerpt ) {

$wpse_excerpt = get_the_content('');

$wpse_excerpt = strip_shortcodes( $wpse_excerpt );

$wpse_excerpt = apply_filters('the_content', $wpse_excerpt);

$wpse_excerpt = str_replace(']]>', ']]>', $wpse_excerpt);

$wpse_excerpt = strip_tags($wpse_excerpt, wpse_allowedtags()); /*IF you need to allow just certain tags. Delete if all tags are allowed */

//Set the excerpt word count and only break after sentence is complete.

$excerpt_word_count = 75;

$excerpt_length = apply_filters('excerpt_length', $excerpt_word_count);

$tokens = array();

$excerptOutput = '';

$count = 0;

// Divide the string into tokens; HTML tags, or words, followed by any whitespace

preg_match_all('/(<[^>]+>|[^<>s]+)s*/u', $wpse_excerpt, $tokens);

foreach ($tokens[0] as $token) {

if ($count >= $excerpt_length && preg_match('/[,;?.!]s*$/uS', $token)) {

// Limit reached, continue until , ; ? . or ! occur at the end

$excerptOutput .= trim($token);

break;

}

// Add words to complete sentence

$count++;

// Append what's left of the token

$excerptOutput .= $token;

}

$wpse_excerpt = trim(force_balance_tags($excerptOutput));

$excerpt_end = ' <a href="'. esc_url( get_permalink() ) . '">' . ' » ' . sprintf(__( 'Read more about: %s  »', 'wpse' ), get_the_title()) . '</a>';

$excerpt_more = apply_filters('excerpt_more', ' ' . $excerpt_end);

//$pos = strrpos($wpse_excerpt, '</');

//if ($pos !== false)

// Inside last HTML tag

//$wpse_excerpt = substr_replace($wpse_excerpt, $excerpt_end, $pos, 0); /* Add read more next to last word */

//else

// After the content

$wpse_excerpt .= $excerpt_more; /*Add read more in new paragraph */

return $wpse_excerpt;

}

return apply_filters('wpse_custom_wp_trim_excerpt', $wpse_excerpt, $raw_excerpt);

}

endif;

remove_filter('get_the_excerpt', 'wp_trim_excerpt');

add_filter('get_the_excerpt', 'wpse_custom_wp_trim_excerpt');