Empty elements can be denoted by a special shorthand tag.
1	Empty	empty	ADJ	POS	Degree=Pos	2	amod	_	_
2	elements	element	NOUN	PL-NOM	Number=Plur	5	nsubj:pass	_	_
3	can	can	AUX	PRES-AUX	VerbForm=Fin	5	aux	_	_
4	be	be	AUX	INF	VerbForm=Inf	5	aux:pass	_	_
5	denoted	denote	VERB	PASS	Tense=Past|VerbForm=Part|Voice=Pass	0	root	_	_
6	by	by	ADP	_	_	10	case	_	_
7	a	a	DET	IND-SG	Definite=Ind|PronType=Art	10	det	_	_
8	special	special	ADJ	POS	Degree=Pos	9	amod	_	_
9	shorthand	shorthand	NOUN	SG-NOM	Number=Sing	10	compound	_	_
10	tag	tag	NOUN	SG-NOM	Number=Sing	5	obl	_	SpaceAfter=No
11	.	.	PUNCT	Period	_	5	punct	_	_
