filters – operate to point out youtube movies inside excerpt – if situation and apply_filters

I’m utilizing WordPress Underscores theme. I wanted to point out movies inside excerpts on weblog web page. I used to be in a position to modify this operate Permit HTML in excerpt to point out youtube movies inside excerpts like so:

my content material.php makes use of the_excerpt();

my operate.php

 operate wpse_allowedtags()
{
  // Add customized tags to this string
  return '<determine>,<iframe>,<p>,<video>';
}

if (!function_exists('wpse_custom_wp_trim_excerpt')) :

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

      $wpse_excerpt = get_the_content('');
      $wpse_excerpt = apply_filters('the_content', $wpse_excerpt);
      $wpse_excerpt = strip_tags($wpse_excerpt, wpse_allowedtags()); /*If it's essential enable simply sure tags. Delete if all tags are allowed */

      //Set the excerpt phrase depend and solely break after sentence is full.
      $excerpt_word_count = 30;
      $excerpt_length = apply_filters('excerpt_length', $excerpt_word_count);
      $tokens = array();
      $excerptOutput="";
      $depend = 0;

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

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

      if ($depend >= $excerpt_length && preg_match('/[;?.!]s*$/uS', $token)) {
          // Restrict reached, proceed till , ; ? . or ! happen on the finish
        $excerptOutput .= trim($token);
          break;
        }

        // Add phrases to finish sentence
         $depend++;

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

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

     
      $excerpt_end = '...'; /*** MODIFY THIS. change the excerpt endind to one thing else.***/
      $excerpt_more = apply_filters('excerpt_more', ' ' . $excerpt_end);

      $pos = strrpos($wpse_excerpt, '</');
      if ($pos !== false)
      // Inside final HTML tag
      $wpse_excerpt = substr_replace($wpse_excerpt, $excerpt_end, $pos, 0); /* Add learn extra subsequent to final phrase */
      else
      // After the content material
      $wpse_excerpt .= $excerpt_more; /*Add learn extra 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');

 

I do not know a lot of PHP however I used to be in a position to google and perceive some parts of the code above. Nevertheless, I’m not positive I absolutely perceive the next:

1. Within the following if situation do these single quotes '' characterize an empty string? If that’s the case, why do we want an empty string ?

$raw_excerpt = $wpse_excerpt;
if ('' == $wpse_excerpt)

2. Based on https://developer.wordpress.org/reference/features/apply_filters/ the third parameter $raw_excerpt within the following operate is $args which is a required parameter. Why do we have to embody it? What it does precisely within the code above?

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