XSD。如何限制单词的首字母大写

import re

def restrict_capitalized(word):
    # 使用正则表达式匹配首字母大写的单词
    pattern = r'\b[A-Z][a-zA-Z]*\b'
    capitalized_words = re.findall(pattern, word)

    # 将首字母大写的单词替换为小写
    for capitalized_word in capitalized_words:
        word = word.replace(capitalized_word, capitalized_word.lower())

    return word

# 示例用法
word = "XSD"
restricted_word = restrict_capitalized(word)
print(restricted_word)  # 输出：xsd