According to the guidelines, an adjective used as a noun is still tagged as an adjective. Eg, the wealthy, the sick, etc. Using that guideline, there's a tagging error for "wealthy" in the following sentence:
# sent_id = GUM_voyage_merida-18
# s_type = decl
# text = The wealthy constructed the grand Pasejo Montejo avenue north of the old town, inspired by the Champs-Élysées in Paris.
1 The the DET DT Definite=Def|PronType=Art 2 det 2:det Discourse=joint:25->24|Entity=(person-50
2 wealthy wealthy NOUN NNS Number=Plur 3 nsubj 3:nsubj Entity=person-50)
3 constructed construct VERB VBD Mood=Ind|Number=Plur|Person=3|Tense=Past|VerbForm=Fin 0 root 0:root _
4 the the DET DT Definite=Def|PronType=Art 8 det 8:det Entity=(place-51-Paseo_de_Montejo
5 grand grand ADJ JJ Degree=Pos 8 amod 8:amod _
6 Pasejo Pasejo PROPN NNP Number=Sing 8 compound 8:compound _
7 Montejo Montejo PROPN NNP Number=Sing 6 flat 6:flat Entity=(person-32-Francisco_de_Montejo_the_Younger)
8 avenue avenue NOUN NN Number=Sing 3 obj 3:obj Entity=place-51-Paseo_de_Montejo)
9 north north ADV RB Degree=Pos 3 advmod 3:advmod _
10 of of ADP IN _ 13 case 13:case _
11 the the DET DT Definite=Def|PronType=Art 13 det 13:det Bridge=place-1-Mérida%2C_Yucatán<place-52-Mérida%2C_Yucatán|Entity=(place-52-Mérida%2C_Yucatán
12 old old ADJ JJ Degree=Pos 13 amod 13:amod _
13 town town NOUN NN Number=Sing 9 nmod 9:nmod:of Entity=place-52-Mérida%2C_Yucatán)|SpaceAfter=No
14 , , PUNCT , _ 15 punct 15:punct _
15 inspired inspire VERB VBN Tense=Past|VerbForm=Part 13 acl 13:acl Discourse=elaboration:26->25
16 by by ADP IN _ 18 case 18:case _
17 the the DET DT Definite=Def|PronType=Art 18 det 18:det Entity=(place-53-Champs-Élysées
18 Champs-Élysées Champs-Élysées PROPN NNP Number=Sing 15 obl 15:obl:by _
19 in in ADP IN _ 20 case 20:case _
20 Paris Paris PROPN NNP Number=Sing 15 obl 15:obl:in Entity=(place-54-Paris)place-53-Champs-Élysées)|SpaceAfter=No
21 . . PUNCT . _ 3 punct 3:punct _
According to the guidelines, an adjective used as a noun is still tagged as an adjective. Eg, the wealthy, the sick, etc. Using that guideline, there's a tagging error for "wealthy" in the following sentence: