Question: when did boxing day become a bank holiday
[{'answer': '1871', 'provenance': [{'wikipedia_id': '4681', 'title': 'Boxing Day', 'start_paragraph_id': 13, 'start_character': 52, 'end_paragraph_id': 13, 'end_character': 56, 'bleu_score': 1.0, 'section': 'Section::::Status by country.\n'}]}]