Hope for a regular expression

Help me read a regular expression & lt; a (s * [^ & gt;] + s *) href = ([\ & quot; | ']?) ([^ \ & Quot; '& gt; \ s] +) ([\ & quot; |']?) /Ies cannot understand the last few letters. please explain it. I is case-insensitive. e. if this modifier is set, preg_replace () helps you read a regular expression.
] + S *) href = ([\ "| ']?) ([^ \ "'> \ S] +) ([\" |']?) /Ies

I can't understand the last few letters.


------ Solution --------------------
I is case insensitive

E if this modifier is set, preg_replace () replaces the reverse reference in the replacement string as a normal replacement, evaluate it as the PHP code, and use the result to replace the searched string.

S's default "." indicates that any character except the line break will become any character, that is, including the line break.

I deleted the post and discussed the technology. if you have any suggestions, please go to the relevant sections of the community.