Regular Expressions 101

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`
(?m)^bar:(?:\n\s.)+
`
gm
(?m)
match the remainder of the pattern with the following effective flags: gm
m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
^ asserts position at start of a line
bar: matches the characters bar: literally (case sensitive)
Non-capturing group
(?:\n\s.)+
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
\n matches a line-feed (newline) character (ASCII 10)
\s
matches any whitespace character (equivalent to [\r\n\t\f\v ])
{4} matches the previous token exactly 4 times
.
matches any character (except for line terminators)
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
Global pattern flags
g modifier: global. All matches (don't return after first match)
m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
Your regular expression does not match the subject string.

Regular Expression
No Match

`
`
gm

Test String