Usual read mode. In this mode the default (empty) value is created by TDeserializer, then the serialized data is read into this default temporary value, and then the value is returned to the user, or assigned to a field/property; thus the property should be assignable (read-write) to be used in this mode.

If the type of value is object type, then new object instance will be created during de-serialization.

Fill-read mode. The converter working in fill-read mode should not modify the value itself. It can use the value only as a constant-reference to some data. In this mode TDeserializer read the value from field or property and use it as a reference to data into which read de-serialization will be performed.

If the type of value is object type, then no new object instance will be created during de-serialization.

For complite description of the fill-read mode read FillReadAttribute description.