Required Text. Specifies the field ID of the column that this FieldRef element references. The field ID is the string representation ...

Required Text. Specifies the field ID of the column that this FieldRef element references. The field ID is the string representation of a GUID, including braces. The value is case sensitive.
You can find the IDs for built-in fields in the file fieldswss.xml located on the following path: %ProgramFiles%\Common Files\Microsoft Shared\web server extensions\14	EMPLATE\FEATURES\fields.

Required assemblies 'WindowsBase', 'PresentationCore', and 'PresentationFramework' are missing from the target framework. ... Required Boolean. If TRUE, the field must have value assigned to it before an item that is created using this content type ... Required if reference element is specified for an Assembly reference. This tag supports both simple text and strong name ... Required Text. Specifies the content type name. The value can be a reference to a resource in the format $Resources:String. ... Required Text. Specifies the field ID of the column that this FieldRef element references. The field ID is the string representation ... Required Text. The displayed name for the column. Maximum length is 255 characters. The value of this attribute is used as ... Required Text. The name of a column. This is the internal name of a column and is guaranteed never to change for the lifetime ... Required Text. The name of a field. This is the internal name of a field and is guaranteed never to change for the lifetime ... Requirement Status by Config: Helps the team identify gaps in test coverage for each test configuration for each requirement. ...