Regular Expressions 101

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/
hello[\n|\s|\S]world
/
gm
hello
matches the characters hello literally (case sensitive)
Match a single character present in the list below
[\n|\s|\S]
\n matches a line-feed (newline) character (ASCII 10)
| matches the character | with index 12410 (7C16 or 1748) literally (case sensitive)
\s matches any whitespace character (equivalent to [\r\n\t\f\v \u00a0\u1680\u2000-\u200a\u2028\u2029\u202f\u205f\u3000\ufeff])
| matches the character | with index 12410 (7C16 or 1748) literally (case sensitive)
\S matches any non-whitespace character (equivalent to [^\r\n\t\f\v \u00a0\u1680\u2000-\u200a\u2028\u2029\u202f\u205f\u3000\ufeff])
world
matches the characters world literally (case sensitive)
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