Regular Expressions 101

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/
<iframe[^>]*?title=(\\\'|\\"|[\'"])([^>]*?)\1
/
gm
<iframe
matches the characters <iframe literally (case sensitive)
Match a single character not present in the list below
[^>]
*? matches the previous token between zero and unlimited times, as few times as possible, expanding as needed (lazy)
> matches the character > with index 6210 (3E16 or 768) literally (case sensitive)
title=
matches the characters title= literally (case sensitive)
1st Capturing Group
(\\\'|\\"|[\'"])
1st Alternative
\\\'
\\ matches the character \ with index 9210 (5C16 or 1348) literally (case sensitive)
\' matches the character ' with index 3910 (2716 or 478) literally (case sensitive)
2nd Alternative
\\"
\\ matches the character \ with index 9210 (5C16 or 1348) literally (case sensitive)
" matches the character " with index 3410 (2216 or 428) literally (case sensitive)
3rd Alternative
[\'"]
Match a single character present in the list below
[\'"]
\' matches the character ' with index 3910 (2716 or 478) literally (case sensitive)
" matches the character " with index 3410 (2216 or 428) literally (case sensitive)
2nd Capturing Group
([^>]*?)
Match a single character not present in the list below
[^>]
*? matches the previous token between zero and unlimited times, as few times as possible, expanding as needed (lazy)
> matches the character > with index 6210 (3E16 or 768) literally (case sensitive)
\1 matches the same text as most recently matched by the 1st capturing group
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.Try launching the debugger to find out why.

Regular Expression
No Match

/
/
gm

Test String

Code Generator

Generated Code

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Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report.
For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php