diff --git a/Michelf/Markdown.php b/Michelf/Markdown.php
index e9b61e8..2d22ce5 100644
--- a/Michelf/Markdown.php
+++ b/Michelf/Markdown.php
@@ -1659,7 +1659,7 @@ class _MarkdownExtra_TmpImpl extends \Michelf\Markdown {
 		if (empty($attr)) return "";
 		
 		# Split on components
-		preg_match_all("/[.#][-_:a-zA-Z0-9]+/", $attr, $matches);
+		preg_match_all('/[#.][-_:a-zA-Z0-9]+/', $attr, $matches);
 		$elements = $matches[0];
 
 		# handle classes and ids (only first id taken into account)
@@ -1811,7 +1811,7 @@ class _MarkdownExtra_TmpImpl extends \Michelf\Markdown {
 					[ ]{0,'.($indent+3).'}~{3,}
 									[ ]*
 					(?:
-						[.]?[-_:a-zA-Z0-9]+ # standalone class name
+					\.?[-_:a-zA-Z0-9]+ # standalone class name
 					|
 						'.$this->id_class_attr_nocatch_re.' # extra attributes
 					)?
@@ -2407,7 +2407,7 @@ class _MarkdownExtra_TmpImpl extends \Michelf\Markdown {
 			(?>\A\n?|\n\n+)					# leading line
 			(								# definition terms = $1
 				[ ]{0,'.$less_than_tab.'}	# leading whitespace
-				(?![:][ ]|[ ])				# negative lookahead for a definition 
+				(?!\:[ ]|[ ])				# negative lookahead for a definition
 											#   mark (colon) or more whitespace.
 				(?> \S.* \n)+?				# actual term (not whitespace).	
 			)			
@@ -2421,12 +2421,12 @@ class _MarkdownExtra_TmpImpl extends \Michelf\Markdown {
 			\n(\n+)?						# leading line = $1
 			(								# marker space = $2
 				[ ]{0,'.$less_than_tab.'}	# whitespace before colon
-				[:][ ]+						# definition mark (colon)
+				\:[ ]+						# definition mark (colon)
 			)
 			((?s:.+?))						# definition text = $3
 			(?= \n+ 						# stop at next definition mark,
 				(?:							# next term or end of text
-					[ ]{0,'.$less_than_tab.'} [:][ ]	|
+					[ ]{0,'.$less_than_tab.'} \:[ ]	|
 					<dt> | \z
 				)						
 			)					
@@ -2482,7 +2482,7 @@ class _MarkdownExtra_TmpImpl extends \Michelf\Markdown {
 				)
 				[ ]*
 				(?:
-					[.]?([-_:a-zA-Z0-9]+) # 2: standalone class name
+					\.?([-_:a-zA-Z0-9]+) # 2: standalone class name
 				|
 					'.$this->id_class_attr_catch_re.' # 3: Extra attributes
 				)?