Part of the Settings API. Outputs a div for each error retrieved by get_settings_errors().
This is called automatically after a settings page based on the Settings API is submitted. Errors should be added during the validation callback function for a setting defined in register_setting().
The $sanitize option is passed into get_settings_errors() and will re-run the setting sanitization on its current value.
The $hide_on_update option will cause errors to only show when the settings page is first loaded. if the user has already saved new values it will be hidden to avoid repeating messages already shown in the default error reporting after submission. This is useful to show general errors like missing settings when the user arrives at the settings page.