This is perfectly legal!!
1	This	this	PRON	DT	Number=Sing|PronType=Dem	4	nsubj	4:nsubj	_
2	is	be	AUX	VBZ	Mood=Ind|Number=Sing|Person=3|Tense=Pres|VerbForm=Fin	4	cop	4:cop	_
3	perfectly	perfectly	ADV	RB	_	4	advmod	4:advmod	_
4	legal	legal	ADJ	JJ	Degree=Pos	0	root	0:root	SpaceAfter=No
5	!!	!!	PUNCT	.	_	4	punct	4:punct	_
