Regular Expressions 101

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"
(?:^|\s)\S
"
gmi
Non-capturing group
(?:^|\s)
1st Alternative
^
^ asserts position at start of a line
2nd Alternative
\s
\s matches any whitespace character (equivalent to [\r\n\t\f\v ])
\S matches any non-whitespace character (equivalent to [^\r\n\t\f\v ])
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)
i modifier: insensitive. Case insensitive match (ignores case of [a-zA-Z])
Your regular expression does not match the subject string.

Regular Expression
No Match

"
"
gmi

Test String

Substitution

Processing...