我找到了这个关于正则表达式的教程，虽然我直观地理解了“greedy”，“勉强”和“possession”限定词的作用，但我的理解中似乎有一个严重的漏洞。
具体来说，在下面的例子中:
Enter your regex: .*foo // Greedy qualifier
Enter input string to search: xfooxxxxxxfoo
I found the text "xfooxxxxxxfoo" starting at index 0 and ending at index 13.
Enter your regex: .*?foo // Reluctant qualifier
Enter input string to search: xfooxxxxxxfoo
I found the text "xfoo" starting at index 0 and ending at index 4.
I found the text "xxxxxxfoo" starting at index 4 and ending at index 13.
Enter your regex: .*+foo // Possessive qualifier
Enter input string to search: xfooxxxxxxfoo
No match found.
解释提到了吃掉整个输入字符串，字母被消耗，匹配器后退，最右边出现的“foo”被反流，等等。
不幸的是，尽管有这些美好的比喻，我还是不明白谁吃什么……您是否知道其他教程(简要地)解释正则表达式引擎如何工作?
或者，如果有人能用不同的措辞解释下一段，那将是非常感激的:
The first example uses the greedy quantifier .* to find "anything", zero or more times, followed by the letters "f", "o", "o". Because the quantifier is greedy, the .* portion of the expression first eats the entire input string. At this point, the overall expression cannot succeed, because the last three letters ("f", "o", "o") have already been consumed [by whom?]. So the matcher slowly backs off [from right-to-left?] one letter at a time until the rightmost occurrence of "foo" has been regurgitated [what does this mean?], at which point the match succeeds and the search ends.
The second example, however, is reluctant, so it starts by first consuming [by whom?] "nothing". Because "foo" doesn't appear at the beginning of the string, it's forced to swallow [who swallows?] the first letter (an "x"), which triggers the first match at 0 and 4. Our test harness continues the process until the input string is exhausted. It finds another match at 4 and 13.
The third example fails to find a match because the quantifier is possessive. In this case, the entire input string is consumed by .*+ [how?], leaving nothing left over to satisfy the "foo" at the end of the expression. Use a possessive quantifier for situations where you want to seize all of something without ever backing off [what does back off mean?]; it will outperform the equivalent greedy quantifier in cases where the match is not immediately found.