Regular Expressions 101

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"
\s+\\\[\s*(?P<brace_bloc>.*?)\s*\\\]\s+
"
gms
\s
matches any whitespace character (equivalent to [\r\n\t\f\v  ])
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
\\ matches the character \ with index 9210 (5C16 or 1348) literally (case sensitive)
\[ matches the character [ with index 9110 (5B16 or 1338) literally (case sensitive)
\s
matches any whitespace character (equivalent to [\r\n\t\f\v  ])
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
Named Capture Group brace_bloc
(?P<brace_bloc>.*?)
.
matches any character
*? matches the previous token between zero and unlimited times, as few times as possible, expanding as needed (lazy)
\s
matches any whitespace character (equivalent to [\r\n\t\f\v  ])
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
\\ matches the character \ with index 9210 (5C16 or 1348) literally (case sensitive)
\] matches the character ] with index 9310 (5D16 or 1358) literally (case sensitive)
\s
matches any whitespace character (equivalent to [\r\n\t\f\v  ])
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
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)
s modifier: single line. Dot matches newline characters
Your regular expression does not match the subject string.

Regular Expression
No Match

r"
"
gms

Test String