Question: when did visors become mandatory in the nhl
[{'answer': '2013', 'provenance': [{'wikipedia_id': '568175', 'title': 'Hockey helmet', 'start_paragraph_id': 4, 'start_character': 197, 'end_paragraph_id': 4, 'end_character': 201, 'bleu_score': 1.0, 'section': 'Section::::Visors and shields.\n'}]}, {'provenance': [{'wikipedia_id': '568175', 'title': 'Hockey helmet', 'start_paragraph_id': 4, 'start_character': 0, 'end_paragraph_id': 4, 'end_character': 291, 'bleu_score': 0.6581433215304421, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1059212448854785705}, 'section': 'Section::::Visors and shields.\n'}]}]