^start of line
.*any Unicode character, repeated any number of times
Subject:the literal text Subject: (case sensitive) .*?any Unicode character, repeated any number of times
\na line-feed (newline) character (ASCII 10)
Group Message(?P<Message>.*) .*any Unicode character, repeated any number of times
^start of line
Onthe literal text On (case sensitive) .*any Unicode character, repeated any number of times
wrote:the literal text wrote: (case sensitive) \na line-feed (newline) character (ASCII 10)
.*any Unicode character, repeated any number of times
g modifier: global. Finds all matches instead of stopping after the first
m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string
s modifier: single line. Allows a dot to match line terminators