- * Since WordPress 1.5.1, bound callbacks can take as many arguments as are
- * passed as parameters in the corresponding apply_filters() call. The `$accepted_args`
- * parameter allows for calling functions only when the number of args match.
+ * Bound callbacks can accept from none to the total number of arguments passed as parameters
+ * in the corresponding apply_filters() call.
+ *
+ * In other words, if an apply_filters() call passes four total arguments, callbacks bound to
+ * it can accept none (the same as 1) of the arguments or up to four. The important part is that
+ * the `$accepted_args` value must reflect the number of arguments the bound callback *actually*
+ * opted to accept. If no arguments were accepted by the callback that is considered to be the
+ * same as accepting 1 argument. For example:
+ *
+ * // Filter call.
+ * $value = apply_filters( 'hook', $value, $arg2, $arg3 );
+ *
+ * // Accepting zero/one arguments.
+ * function example_callback() {
+ * ...
+ * return 'some value';
+ * }
+ * add_filter( 'hook', 'example_callback' ); // Where $priority is default 10, $accepted_args is default 1.
+ *
+ * // Accepting two arguments (three possible).
+ * function example_callback( $value, $arg2 ) {
+ * ...
+ * return $maybe_modified_value;
+ * }
+ * add_filter( 'hook', 'example_callback', 10, 2 ); // Where $priority is 10, $accepted_args is 2.