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<?php $line = 'You know this brother has knowledge of brotherhood.'; $pattern = '~\b(Know|brother)\b~i'; $output = preg_replace($pattern, '<b>$1</b>', $line); var_dump(trim($output));
Output for 7.4.0 - 7.4.33, 8.0.1 - 8.0.30, 8.1.0 - 8.1.34, 8.2.0 - 8.2.30, 8.3.0 - 8.3.30, 8.4.1 - 8.4.18, 8.5.0 - 8.5.3
string(65) "You <b>know</b> this <b>brother</b> has knowledge of brotherhood."

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