Sentence:  When we have clitic doubling constructions (with both a full NP and a clitic), the NP needs a dummy <WSD>Case</WSD> marker in order to get <WSD>Case</WSD>, as its “normal” <WSD>Case</WSD> is absorbed by the clitic, otherwise it will be ruled out by the <WSD>Case</WSD> Filter. It must be stressed that ‘<WSD>Case</WSD>' here is abstract <WSD>Case</WSD> (written with capital C), a licencing requirement making arguments visible for θ-marking, and not morphological case. 
Meaning of the word marked with <WSD> tags:  abstract feature of a noun phrase that determines its function in a sentence, such as a grammatical case and a position.