***strong em** inside of em* should produce valid markup

Parsedown.php

@@ -779,14 +779,19 @@ class Parsedown
 
 		if (strpos($text, '_') !== FALSE)
 		{
-			$text = preg_replace('/__(?=\S)(.+?)(?<=\S)__(?!_)/s', '<strong>$1</strong>', $text);
+			$text = preg_replace('/__(?=\S)([^_]+?)(?<=\S)__/s', '<strong>$1</strong>', $text, -1, $count);
+			$count or $text = preg_replace('/__(?=\S)(.+?)(?<=\S)__(?!_)/s', '<strong>$1</strong>', $text);
+
 			$text = preg_replace('/\b_(?=\S)(.+?)(?<=\S)_\b/s', '<em>$1</em>', $text);
 		}
 
 		if (strpos($text, '*') !== FALSE)
 		{
-			$text = preg_replace('/\*\*(?=\S)(.+?)(?<=\S)\*\*(?!\*)/s', '<strong>$1</strong>', $text);
-			$text = preg_replace('/\*(?=\S)(.+?)(?<=\S)\*/s', '<em>$1</em>', $text);
+			$text = preg_replace('/\*\*(?=\S)([^*]+?)(?<=\S)\*\*/s', '<strong>$1</strong>', $text, -1, $count);
+			$count or $text = preg_replace('/\*\*(?=\S)(.+?)(?<=\S)\*\*(?!\*)/s', '<strong>$1</strong>', $text);
+
+			$text = preg_replace('/\*(?=\S)([^*]+?)(?<=\S)\*/s', '<em>$1</em>', $text, -1, $count);
+			$count or $text = preg_replace('/\*(?=\S)(.+?)(?<=\S)\*(?!\*)/s', '<em>$1</em>', $text);
 		}
 
 		$text = strtr($text, $map);

tests/data/strong_em.html

+<p><em><strong>strong em</strong></em> </p>
+<p><em>em <strong>strong em</strong></em></p>
+<p><em><strong>strong em</strong> em</em></p>
+<p><em><strong>strong em</strong></em></p>
+<p><em>em <strong>strong em</strong></em></p>
+<p><em><strong>strong em</strong> em</em></p>
\ No newline at end of file

tests/data/strong_em.md

+***strong em*** 
+
+*em **strong em***
+
+***strong em** em*
+
+___strong em___
+
+_em __strong em___
+
+___strong em__ em_
\ No newline at end of file