Regular Expressions 101

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"
(<p>(?=<img\s.*?))(.*?)(</p>)
"
gm
1st Capturing Group
(<p>(?=<img\s.*?))
<p>
matches the characters <p> literally (case sensitive)
Positive Lookahead
(?=<img\s.*?)
Assert that the Regex below matches
<img
matches the characters <img literally (case sensitive)
\s matches any whitespace character (equivalent to [\r\n\t\f\v  ])
.
matches any character (except for line terminators)
*? matches the previous token between zero and unlimited times, as few times as possible, expanding as needed (lazy)
2nd Capturing Group
(.*?)
.
matches any character (except for line terminators)
*? matches the previous token between zero and unlimited times, as few times as possible, expanding as needed (lazy)
3rd Capturing Group
(</p>)
</p>
matches the characters </p> 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

r"
"
gm

Test String

Substitution

Processing...