Regular Expressions 101

Explanation

Pro

^start of line

Non-Capturing Group(?:\n?(?:From|To|Cc|Subject)\s*:.*)+

+repeats the group contents below at least once:

\n?optionally matches a line-feed (newline) character (ASCII 10)

Non-Capturing Group(?:From|To|Cc|Subject)

1st AlternativeFrom

Fromthe literal text From (case sensitive)

2nd AlternativeTo

Tothe literal text To (case sensitive)

3rd AlternativeCc

Ccthe literal text Cc (case sensitive)

4th AlternativeSubject

Subjectthe literal text Subject (case sensitive)

\s*a Unicode whitespace character, repeated any number of times

:the literal : (58₁₀ / 72₈ / 3A₁₆)

.*any Unicode character (except for line terminators), repeated any number of times

\s*a Unicode whitespace character, repeated any number of times

Global pattern flags

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

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25 tokens

^(?:\n?(?:From|To|Cc|Subject)\s*:.*)+\s*

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