the wp_head hook.
 *
 * See {@see 'wp_head'}.
 *
 * @since 2.5.0
 */
function wp_generator() {
	/**
	 * Filters the output of the XHTML generator tag.
	 *
	 * @since 2.5.0
	 *
	 * @param string $generator_type The XHTML generator.
	 */
	the_generator( apply_filters( 'wp_generator_type', 'xhtml' ) );
}

/**
 * Displays the generator XML or Comment for RSS, ATOM, etc.
 *
 * Returns the correct generator type for the requested output format. Allows
 * for a plugin to filter generators overall the {@see 'the_generator'} filter.
 *
 * @since 2.5.0
 *
 * @param string $type The type of generator to output - (html|xhtml|atom|rss2|rdf|comment|export).
 */
function the_generator( $type ) {
	/**
	 * Filters the output of the XHTML generator tag for display.
	 *
	 * @since 2.5.0
	 *
	 * @param string $generator_type The generator output.
	 * @param string $type           The type of generator to output. Accepts 'html',
	 *                               'xhtml', 'atom', 'rss2', 'rdf', 'comment', 'export'.
	 */
	echo apply_filters( 'the_generator', get_the_generator( $type ), $type ) . "\n";
}

/**
 * Creates the generator XML or Comment for RSS, ATOM, etc.
 *
 * Returns the correct generator type for the requested output format. Allows
 * for a plugin to filter generators on an individual basis using the
 * {@see 'get_the_generator_$type'} filter.
 *
 * @since 2.5.0
 *
 * @param string $type The type of generator to return - (html|xhtml|atom|rss2|rdf|comment|export).
 * @return string|void The HTML content for the generator.
 */
function get_the_generator( $type = '' ) {
	if ( empty( $type ) ) {

		$current_filter = current_filter();
		if ( empty( $current_filter ) ) {
			return;
		}

		switch ( $current_filter ) {
			case 'rss2_head':
			case 'commentsrss2_head':
				$type = 'rss2';
				break;
			case 'rss_head':
			case 'opml_head':
				$type = 'comment';
				break;
			case 'rdf_header':
				$type = 'rdf';
				break;
			case 'atom_head':
			case 'comments_atom_head':
			case 'app_head':
				$type = 'atom';
				break;
		}
	}

	switch ( $type ) {
		case 'html':
			$gen = '<meta name="generator" content="WordPress ' . esc_attr( get_bloginfo( 'version' ) ) . '">';
			break;
		case 'xhtml':
			$gen = '<meta name="generator" content="WordPress ' . esc_attr( get_bloginfo( 'version' ) ) . '" />';
			break;
		case 'atom':
			$gen = '<generator uri="https://wordpress.org/" version="' . esc_attr( get_bloginfo_rss( 'version' ) ) . '">WordPress</generator>';
			break;
		case 'rss2':
			$gen = '<generator>' . sanitize_url( 'https://wordpress.org/?v=' . get_bloginfo_rss( 'version' ) ) . '</generator>';
			break;
		case 'rdf':
			$gen = '<admin:generatorAgent rdf:resource="' . sanitize_url( 'https://wordpress.org/?v=' . get_bloginfo_rss( 'version' ) ) . '" />';
			break;
		case 'comment':
			$gen = '<!-- generator="WordPress/' . esc_attr( get_bloginfo( 'version' ) ) . '" -->';
			break;
		case 'export':
			$gen = '<!-- generator="WordPress/' . esc_attr( get_bloginfo_rss( 'version' ) ) . '" created="' . gmdate( 'Y-m-d H:i' ) . '" -->';
			break;
	}

	/**
	 * Filters the HTML for the retrieved generator type.
	 *
	 * The dynamic portion of the hook name, `$type`, refers to the generator type.
	 *
	 * Possible hook names include:
	 *
	 *  - `get_the_generator_atom`
	 *  - `get_the_generator_comment`
	 *  - `get_the_generator_export`
	 *  - `get_the_generator_html`
	 *  - `get_the_generator_rdf`
	 *  - `get_the_generator_rss2`
	 *  - `get_the_generator_xhtml`
	 *
	 * @since 2.5.0
	 *
	 * @param string $gen  The HTML markup output to wp_head().
	 * @param string $type The type of generator. Accepts 'html', 'xhtml', 'atom',
	 *                     'rss2', 'rdf', 'comment', 'export'.
	 */
	return apply_filters( "get_the_generator_{$type}", $gen, $type );
}

/**
 * Outputs the HTML checked attribute.
 *
 * Compares the first two arguments and if identical marks as checked.
 *
 * @since 1.0.0
 *
 * @param mixed $checked One of the values to compare.
 * @param mixed $current Optional. The other value to compare if not just true.
 *                       Default true.
 * @param bool  $display Optional. Whether to echo or just return the string.
 *                       Default true.
 * @return string HTML attribute or empty string.
 */
function checked( $checked, $current = true, $display = true ) {
	return __checked_selected_helper( $checked, $current, $display, 'checked' );
}

/**
 * Outputs the HTML selected attribute.
 *
 * Compares the first two arguments and if identical marks as selected.
 *
 * @since 1.0.0
 *
 * @param mixed $selected One of the values to compare.
 * @param mixed $current  Optional. The other value to compare if not just true.
 *                        Default true.
 * @param bool  $display  Optional. Whether to echo or just return the string.
 *                        Default true.
 * @return string HTML attribute or empty string.
 */
function selected( $selected, $current = true, $display = true ) {
	return __checked_selected_helper( $selected, $current, $display, 'selected' );
}

/**
 * Outputs the HTML disabled attribute.
 *
 * Compares the first two arguments and if identical marks as disabled.
 *
 * @since 3.0.0
 *
 * @param mixed $disabled One of the values to compare.
 * @param mixed $current  Optional. The other value to compare if not just true.
 *                        Default true.
 * @param bool  $display  Optional. Whether to echo or just return the string.
 *                        Default true.
 * @return string HTML attribute or empty string.
 */
function disabled( $disabled, $current = true, $display = true ) {
	return __checked_selected_helper( $disabled, $current, $display, 'disabled' );
}

/**
 * Outputs the HTML readonly attribute.
 *
 * Compares the first two arguments and if identical marks as readonly.
 *
 * @since 5.9.0
 *
 * @param mixed $readonly_value One of the values to compare.
 * @param mixed $current        Optional. The other value to compare if not just true.
 *                              Default true.
 * @param bool  $display        Optional. Whether to echo or just return the string.
 *                              Default true.
 * @return string HTML attribute or empty string.
 */
function wp_readonly( $readonly_value, $current = true, $display = true ) {
	return __checked_selected_helper( $readonly_value, $current, $display, 'readonly' );
}

/*
 * Include a compat `readonly()` function on PHP < 8.1. Since PHP 8.1,
 * `readonly` is a reserved keyword and cannot be used as a function name.
 * In order to avoid PHP parser errors, this function was extracted
 * to a separate file and is only included conditionally on PHP < 8.1.
 */
if ( PHP_VERSION_ID < 80100 ) {
	require_once __DIR__ . '/php-compat/readonly.php';
}

/**
 * Private helper function for checked, selected, disabled and readonly.
 *
 * Compares the first two arguments and if identical marks as `$type`.
 *
 * @since 2.8.0
 * @access private
 *
 * @param mixed  $helper  One of the values to compare.
 * @param mixed  $current The other value to compare if not just true.
 * @param bool   $display Whether to echo or just return the string.
 * @param string $type    The type of checked|selected|disabled|readonly we are doing.
 * @return string HTML attribute or empty string.
 */
function __checked_selected_helper( $helper, $current, $display, $type ) { // phpcs:ignore WordPress.NamingConventions.ValidFunctionName.FunctionDoubleUnderscore,PHPCompatibility.FunctionNameRestrictions.ReservedFunctionNames.FunctionDoubleUnderscore
	if ( (string) $helper === (string) $current ) {
		$result = " $type='$type'";
	} else {
		$result = '';
	}

	if ( $display ) {
		echo $result;
	}

	return $result;
}

/**
 * Assigns a visual indicator for required form fields.
 *
 * @since 6.1.0
 *
 * @return string Indicator glyph wrapped in a `span` tag.
 */
function wp_required_field_indicator() {
	/* translators: Character to identify required form fields. */
	$glyph     = __( '*' );
	$indicator = '<span class="required">' . esc_html( $glyph ) . '</span>';

	/**
	 * Filters the markup for a visual indicator of required form fields.
	 *
	 * @since 6.1.0
	 *
	 * @param string $indicator Markup for the indicator element.
	 */
	return apply_filters( 'wp_required_field_indicator', $indicator );
}

/**
 * Creates a message to explain required form fields.
 *
 * @since 6.1.0
 *
 * @return string Message text and glyph wrapped in a `span` tag.
 */
function wp_required_field_message() {
	$message = sprintf(
		'<span class="required-field-message">%s</span>',
		/* translators: %s: Asterisk symbol (*). */
		sprintf( __( 'Required fields are marked %s' ), wp_required_field_indicator() )
	);

	/**
	 * Filters the message to explain required form fields.
	 *
	 * @since 6.1.0
	 *
	 * @param string $message Message text and glyph wrapped in a `span` tag.
	 */
	return apply_filters( 'wp_required_field_message', $message );
}

/**
 * Default settings for heartbeat.
 *
 * Outputs the nonce used in the heartbeat XHR.
 *
 * @since 3.6.0
 *
 * @param array $settings
 * @return array Heartbeat settings.
 */
function wp_heartbeat_settings( $settings ) {
	if ( ! is_admin() ) {
		$settings['ajaxurl'] = admin_url( 'admin-ajax.php', 'relative' );
	}

	if ( is_user_logged_in() ) {
		$settings['nonce'] = wp_create_nonce( 'heartbeat-nonce' );
	}

	return $settings;
}
ct          $data_object Data model like WP_Term or WP_Post.
	 * @param WP_REST_Request $request     Full details about the request.
	 * @return true|WP_Error True on success, WP_Error object if a field cannot be updated.
	 */
	protected function update_additional_fields_for_object( $data_object, $request ) {
		$additional_fields = $this->get_additional_fields();

		foreach ( $additional_fields as $field_name => $field_options ) {
			if ( ! $field_options['update_callback'] ) {
				continue;
			}

			// Don't run the update callbacks if the data wasn't passed in the request.
			if ( ! isset( $request[ $field_name ] ) ) {
				continue;
			}

			$result = call_user_func(
				$field_options['update_callback'],
				$request[ $field_name ],
				$data_object,
				$field_name,
				$request,
				$this->get_object_type()
			);

			if ( is_wp_error( $result ) ) {
				return $result;
			}
		}

		return true;
	}

	/**
	 * Adds the schema from additional fields to a schema array.
	 *
	 * The type of object is inferred from the passed schema.
	 *
	 * @since 4.7.0
	 *
	 * @param array $schema Schema array.
	 * @return array Modified Schema array.
	 */
	protected function add_additional_fields_schema( $schema ) {
		if ( empty( $schema['title'] ) ) {
			return $schema;
		}

		// Can't use $this->get_object_type otherwise we cause an inf loop.
		$object_type = $schema['title'];

		$additional_fields = $this->get_additional_fields( $object_type );

		foreach ( $additional_fields as $field_name => $field_options ) {
			if ( ! $field_options['schema'] ) {
				continue;
			}

			$schema['properties'][ $field_name ] = $field_options['schema'];
		}

		return $schema;
	}

	/**
	 * Retrieves all of the registered additional fields for a given object-type.
	 *
	 * @since 4.7.0
	 *
	 * @global array $wp_rest_additional_fields Holds registered fields, organized by object type.
	 *
	 * @param string $object_type Optional. The object type.
	 * @return array Registered additional fields (if any), empty array if none or if the object type
	 *               could not be inferred.
	 */
	protected function get_additional_fields( $object_type = null ) {
		global $wp_rest_additional_fields;

		if ( ! $object_type ) {
			$object_type = $this->get_object_type();
		}

		if ( ! $object_type ) {
			return array();
		}

		if ( ! $wp_rest_additional_fields || ! isset( $wp_rest_additional_fields[ $object_type ] ) ) {
			return array();
		}

		return $wp_rest_additional_fields[ $object_type ];
	}

	/**
	 * Retrieves the object type this controller is responsible for managing.
	 *
	 * @since 4.7.0
	 *
	 * @return string Object type for the controller.
	 */
	protected function get_object_type() {
		$schema = $this->get_item_schema();

		if ( ! $schema || ! isset( $schema['title'] ) ) {
			return null;
		}

		return $schema['title'];
	}

	/**
	 * Gets an array of fields to be included on the response.
	 *
	 * Included fields are based on item schema and `_fields=` request argument.
	 *
	 * @since 4.9.6
	 *
	 * @param WP_REST_Request $request Full details about the request.
	 * @return string[] Fields to be included in the response.
	 */
	public function get_fields_for_response( $request ) {
		$schema     = $this->get_item_schema();
		$properties = isset( $schema['properties'] ) ? $schema['properties'] : array();

		$additional_fields = $this->get_additional_fields();

		foreach ( $additional_fields as $field_name => $field_options ) {
			/*
			 * For back-compat, include any field with an empty schema
			 * because it won't be present in $this->get_item_schema().
			 */
			if ( is_null( $field_options['schema'] ) ) {
				$properties[ $field_name ] = $field_options;
			}
		}

		// Exclude fields that specify a different context than the request context.
		$context = $request['context'];
		if ( $context ) {
			foreach ( $properties as $name => $options ) {
				if ( ! empty( $options['context'] ) && ! in_array( $context, $options['context'], true ) ) {
					unset( $properties[ $name ] );
				}
			}
		}

		$fields = array_keys( $properties );

		/*
		 * '_links' and '_embedded' are not typically part of the item schema,
		 * but they can be specified in '_fields', so they are added here as a
		 * convenience for checking with rest_is_field_included().
		 */
		$fields[] = '_links';
		if ( $request->has_param( '_embed' ) ) {
			$fields[] = '_embedded';
		}

		$fields = array_unique( $fields );

		if ( ! isset( $request['_fields'] ) ) {
			return $fields;
		}
		$requested_fields = wp_parse_list( $request['_fields'] );
		if ( 0 === count( $requested_fields ) ) {
			return $fields;
		}
		// Trim off outside whitespace from the comma delimited list.
		$requested_fields = array_map( 'trim', $requested_fields );
		// Always persist 'id', because it can be needed for add_additional_fields_to_object().
		if ( in_array( 'id', $fields, true ) ) {
			$requested_fields[] = 'id';
		}
		// Return the list of all requested fields which appear in the schema.
		return array_reduce(
			$requested_fields,
			static function ( $response_fields, $field ) use ( $fields ) {
				if ( in_array( $field, $fields, true ) ) {
					$response_fields[] = $field;
					return $response_fields;
				}
				// Check for nested fields if $field is not a direct match.
				$nested_fields = explode( '.', $field );
				/*
				 * A nested field is included so long as its top-level property
				 * is present in the schema.
				 */
				if ( in_array( $nested_fields[0], $fields, true ) ) {
					$response_fields[] = $field;
				}
				return $response_fields;
			},
			array()
		);
	}

	/**
	 * Retrieves an array of endpoint arguments from the item schema for the controller.
	 *
	 * @since 4.7.0
	 *
	 * @param string $method Optional. HTTP method of the request. The arguments for `CREATABLE` requests are
	 *                       checked for required values and may fall-back to a given default, this is not done
	 *                       on `EDITABLE` requests. Default WP_REST_Server::CREATABLE.
	 * @return array Endpoint arguments.
	 */
	public function get_endpoint_args_for_item_schema( $method = WP_REST_Server::CREATABLE ) {
		return rest_get_endpoint_args_for_schema( $this->get_item_schema(), $method );
	}

	/**
	 * Sanitizes the slug value.
	 *
	 * @since 4.7.0
	 *
	 * @internal We can't use sanitize_title() directly, as the second
	 * parameter is the fallback title, which would end up being set to the
	 * request object.
	 *
	 * @see https://github.com/WP-API/WP-API/issues/1585
	 *
	 * @todo Remove this in favour of https://core.trac.wordpress.org/ticket/34659
	 *
	 * @param string $slug Slug value passed in request.
	 * @return string Sanitized value for the slug.
	 */
	public function sanitize_slug( $slug ) {
		return sanitize_title( $slug );
	}
}
<br />
<b>Fatal error</b>:  Uncaught Error: Class 'WP_REST_Controller' not found in /home/ocb/public_html/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php:17
Stack trace:
#0 /home/ocb/public_html/wp-settings.php(286): require()
#1 /home/ocb/public_html/wp-config.php(77): require_once('/home/ocb/publi...')
#2 /home/ocb/public_html/wp-load.php(50): require_once('/home/ocb/publi...')
#3 /home/ocb/public_html/wp-blog-header.php(13): require_once('/home/ocb/publi...')
#4 /home/ocb/public_html/index.php(17): require('/home/ocb/publi...')
#5 {main}
  thrown in <b>/home/ocb/public_html/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php</b> on line <b>17</b><br />
<br />
<b>Fatal error</b>:  Uncaught Error: Call to a member function set() on null in /home/ocb/public_html/wp-includes/l10n.php:856
Stack trace:
#0 /home/ocb/public_html/wp-includes/l10n.php(959): load_textdomain('default', '/home/ocb/publi...', 'lv')
#1 /home/ocb/public_html/wp-includes/class-wp-fatal-error-handler.php(49): load_default_textdomain()
#2 [internal function]: WP_Fatal_Error_Handler-&gt;handle()
#3 {main}
  thrown in <b>/home/ocb/public_html/wp-includes/l10n.php</b> on line <b>856</b><br />