$re = '/<(?:[^>=]|=\'[^\']*\'|="[^"]*"|=[^\'"][^\s>]*)*>/i';
$str = '<span data-toggle="tooltip" title="xxx">FUU</span><br><span class="btn btn-outline-secondary font-sm p-1" onclick="bar(event)"><i class="fa fa-bar-chart" aria-hidden="true"></i></span><span data-toggle="tooltip" data-html="true" title="fuu (<b>BAR</b>) is based on fuu.">FUU</span>';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
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