Regular Expressions 101

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/
(\:(\w|\+|\-)+\:)(?=\s|[\!\.\?]|$)
/
gim
1st Capturing Group
(\:(\w|\+|\-)+\:)
\: matches the character : with index 5810 (3A16 or 728) literally (case insensitive)
2nd Capturing Group
(\w|\+|\-)+
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
A repeated capturing group will only capture the last iteration. Put a capturing group around the repeated group to capture all iterations or use a non-capturing group instead if you're not interested in the data
1st Alternative
\w
\w matches any word character (equivalent to [a-zA-Z0-9_])
2nd Alternative
\+
\+ matches the character + with index 4310 (2B16 or 538) literally (case insensitive)
3rd Alternative
\-
\- matches the character - with index 4510 (2D16 or 558) literally (case insensitive)
\: matches the character : with index 5810 (3A16 or 728) literally (case insensitive)
Positive Lookahead
(?=\s|[\!\.\?]|$)
Assert that the Regex below matches
1st Alternative
\s
\s matches any whitespace character (equivalent to [\r\n\t\f\v \u00a0\u1680\u2000-\u200a\u2028\u2029\u202f\u205f\u3000\ufeff])
2nd Alternative
[\!\.\?]
Match a single character present in the list below
[\!\.\?]
\! matches the character ! with index 3310 (2116 or 418) literally (case insensitive)
\. matches the character . with index 4610 (2E16 or 568) literally (case insensitive)
\? matches the character ? with index 6310 (3F16 or 778) literally (case insensitive)
3rd Alternative
$
$ asserts position at the end of a line
Global pattern flags
g modifier: global. All matches (don't return after first match)
i modifier: insensitive. Case insensitive match (ignores case of [a-zA-Z])
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

/
/
gim

Test String