Specifies a field level filter to be performed on the
parent element of the filter element. Restrictions: If the Field element
is present, the Alert Target Meta Type is used to indicate the content
type used in the content filtering and MUST be present. The Item Meta
element is used to indicate the device info mime type and MUST be
present. The Item Data element MUST contain Property elements. The
Property elements MUST be used to override any Property elements
previously received in the CTCap element for the content-type being
filtered and MUST apply to the current synchronization session only. If
no Field element is present in the Filter element, then all properties
SHOULD be filtered using the device info data store CTCap element for
the specified Alert Target element.