Index: wp-includes/category-template.php
===================================================================
--- wp-includes/category-template.php	(revision 20475)
+++ wp-includes/category-template.php	(working copy)
@@ -328,7 +328,7 @@
 
 	$tab_index_attribute = '';
 	if ( (int) $tab_index > 0 )
-		$tab_index_attribute = " tabindex=\"$tab_index\"";
+		$tab_index_attribute = ' tabindex="' . $tab_index .'"';
 
 	$categories = get_terms( $taxonomy, $r );
 	$name = esc_attr( $name );
@@ -336,13 +336,13 @@
 	$id = $id ? esc_attr( $id ) : $name;
 
 	if ( ! $r['hide_if_empty'] || ! empty($categories) )
-		$output = "<select name='$name' id='$id' class='$class' $tab_index_attribute>\n";
+		$output = '<select name="' . $name . '" id="' . $id . '" class="' . $class . '" ' . $tab_index_attribute . '>' . "\n";
 	else
 		$output = '';
 
 	if ( empty($categories) && ! $r['hide_if_empty'] && !empty($show_option_none) ) {
 		$show_option_none = apply_filters( 'list_cats', $show_option_none );
-		$output .= "\t<option value='-1' selected='selected'>$show_option_none</option>\n";
+		$output .= "\t" . '<option value="-1" selected="selected">' . $show_option_none . '</option>' . "\n";
 	}
 
 	if ( ! empty( $categories ) ) {
@@ -350,13 +350,13 @@
 		if ( $show_option_all ) {
 			$show_option_all = apply_filters( 'list_cats', $show_option_all );
 			$selected = ( '0' === strval($r['selected']) ) ? " selected='selected'" : '';
-			$output .= "\t<option value='0'$selected>$show_option_all</option>\n";
+			$output .= "\t" . '<option value="0"' . $selected . '>' . $show_option_all . '</option>' . "\n";
 		}
 
 		if ( $show_option_none ) {
 			$show_option_none = apply_filters( 'list_cats', $show_option_none );
 			$selected = ( '-1' === strval($r['selected']) ) ? " selected='selected'" : '';
-			$output .= "\t<option value='-1'$selected>$show_option_none</option>\n";
+			$output .= "\t" . '<option value="-1"' . $selected . '>' . $show_option_none . '</option>'. "\n";
 		}
 
 		if ( $hierarchical )