Default configuration can be defined by a module, theme, or installation profile in its <em>config/install</em> or <em>config/optional</em> directories. Configuration is provided in YAML files (file extension .yml); YAML is a human-readable data serialization standard that is used by the core software for several purposes. Once the default configuration has been imported into the site's active configuration (through installing the extension), that configuration is owned by the site, not the extension. This means that future updates of the extension will not override the site's active configuration for that extension.