问一下这个代码是什么思路（编译有点问题

找到所有以x或x开头的单词，并输出它们的位置
Input: w
Input: “When you are down and out, remember to keep your head up. When you are up and well, remember to keep your feet down.”
Output:
When : (1, 5)
When : (59, 63)
well : (79, 83)

import re
st=input()#w
pa='\\b(?i)'+st+'\\w+\\b'
pattern = re.compile(pa)
exampleString=input()
index = 0
while True:
    matchResult = pattern.search(exampleString,index)
    if not matchResult:
       break
    print(matchResult.group(0),'.',matchResult.span(0))
    index=matchResult.end(0)

没看懂题目什么意思