The behavior of fields can be controlled by their configuration - or as we call it in our API: their field setting. The field setting of a field contains properties that define the behavior of the field - for example a field can be configured as read only or required. The field setting of fields can be adjusted in the content type definition (CTD), using the Configuration element.
As fields build up content, the set of Fields are defined when content types are defined. The CTD holds the field definition information (besides a couple of content type-related configuration settings). When defining a content type the contained fields can be defined in the CTD with XML fragments describing the type of the field, metadata and field setting.
Field setting and field types
Different Field types have different Field Settings. Besides Field type-specific settings there are a couple common settings that are available for all Fields. For a complete list of common Field Setting configuration properties see CTD field definition