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run code in 150+ php & hhvm versions
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<?php echo preg_replace(array('/\s{2,}/', '/[\n]/'), '', '<h1> A headline like it would be formatted by an IDE </h1>');
based on riCBZ
Output for 4.3.0 - 7.1.0
<h1>A headline like it would be formatted by an IDE</h1>