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   1  <?php
   2  /**
   3   * Filter Sentinel API.
   4   *
   5   * @package WordPress
   6   * @since 7.1.0
   7   */
   8  
   9  declare( strict_types = 1 );
  10  
  11  /**
  12   * Marker object used as a filter's default value when any user value — including
  13   * `null`, `false`, or arbitrary objects — must remain distinguishable from the
  14   * "no filter modified this" case.
  15   *
  16   * Each instance is unique by identity. Compare returned values with `===` against
  17   * the original sentinel to detect that no filter callback replaced it.
  18   *
  19   * Filter callbacks that want to pass through without modifying the value should
  20   * return the received value unchanged. Returning a freshly constructed
  21   * `WP_Filter_Sentinel` is treated as a replacement, not as pass-through.
  22   *
  23   * @since 7.1.0
  24   */
  25  final class WP_Filter_Sentinel {}