Regular Expressions 101

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"
(?<!^|\n|[.!?] )[A-Z\d][A-Za-z\d]*(?: (?:of )?[A-Z\d][A-Za-z\d]*)*
"
g
All the errors detected are listed below, from left to right, as they appear in the pattern.
(?<! A lookbehind assertion has to be fixed width
) A lookbehind assertion has to be fixed width
Your regular expression does not match the subject string.

Regular Expression
No Match

r"
"
g

Test String