diff --git a/wp-includes/class.wp-scripts.php b/wp-includes/class.wp-scripts.php
index ae0148ee8d..988ba792b0 100644
--- a/wp-includes/class.wp-scripts.php
+++ b/wp-includes/class.wp-scripts.php
@@ -95,15 +95,25 @@ class WP_Scripts extends WP_Dependencies {
 		if ( false === $group && in_array($handle, $this->in_footer, true) )
 			$this->in_footer = array_diff( $this->in_footer, (array) $handle );
 
-		if ( null === $this->registered[$handle]->ver )
+		$obj = $this->registered[$handle];
+
+		if ( null === $obj->ver ) {
 			$ver = '';
-		else
-			$ver = $this->registered[$handle]->ver ? $this->registered[$handle]->ver : $this->default_version;
+		} else {
+			$ver = $obj->ver ? $obj->ver : $this->default_version;
+		}
 
 		if ( isset($this->args[$handle]) )
 			$ver = $ver ? $ver . '&' . $this->args[$handle] : $this->args[$handle];
 
-		$src = $this->registered[$handle]->src;
+		$src = $obj->src;
+		$cond_before = $cond_after = '';
+		$conditional = isset( $obj->extra['conditional'] ) ? $obj->extra['conditional'] : '';
+
+		if ( $conditional ) {
+			$cond_before = "<!--[if {$conditional}]>\n";
+			$cond_after = "<![endif]-->\n";
+		}
 
 		if ( $this->do_concat ) {
 			/**
@@ -115,7 +125,7 @@ class WP_Scripts extends WP_Dependencies {
 			 * @param string $handle Script handle.
 			 */
 			$srce = apply_filters( 'script_loader_src', $src, $handle );
-			if ( $this->in_default_dir($srce) ) {
+			if ( $this->in_default_dir( $srce ) && ! $conditional ) {
 				$this->print_code .= $this->print_extra_script( $handle, false );
 				$this->concat .= "$handle,";
 				$this->concat_version .= "$handle$ver";
@@ -126,13 +136,24 @@ class WP_Scripts extends WP_Dependencies {
 			}
 		}
 
+		$has_conditional_data = $conditional && $this->get_data( $handle, 'data' );
+
+		if ( $has_conditional_data ) {
+			echo $cond_before;
+		}
+
 		$this->print_extra_script( $handle );
-		if ( !preg_match('|^(https?:)?//|', $src) && ! ( $this->content_url && 0 === strpos($src, $this->content_url) ) ) {
+
+		if ( $has_conditional_data ) {
+			echo $cond_after;
+		}
+
+		if ( ! preg_match( '|^(https?:)?//|', $src ) && ! ( $this->content_url && 0 === strpos( $src, $this->content_url ) ) ) {
 			$src = $this->base_url . $src;
 		}
 
-		if ( !empty($ver) )
-			$src = add_query_arg('ver', $ver, $src);
+		if ( ! empty( $ver ) )
+			$src = add_query_arg( 'ver', $ver, $src );
 
 		/** This filter is documented in wp-includes/class.wp-scripts.php */
 		$src = esc_url( apply_filters( 'script_loader_src', $src, $handle ) );
@@ -140,7 +161,7 @@ class WP_Scripts extends WP_Dependencies {
 		if ( ! $src )
 			return true;
 
-		$tag = "<script type='text/javascript' src='$src'></script>\n";
+		$tag = "{$cond_before}<script type='text/javascript' src='$src'></script>\n{$cond_after}";
 
 		/**
 		 * Filter the HTML script tag of an enqueued script.
diff --git a/wp-includes/functions.wp-scripts.php b/wp-includes/functions.wp-scripts.php
index afa46be271..9fd5d87d80 100644
--- a/wp-includes/functions.wp-scripts.php
+++ b/wp-includes/functions.wp-scripts.php
@@ -271,3 +271,25 @@ function wp_script_is( $handle, $list = 'enqueued' ) {
 
 	return (bool) wp_scripts()->query( $handle, $list );
 }
+
+/**
+ * Add metadata to a script.
+ *
+ * Works only if the script has already been added.
+ *
+ * Possible values for $key and $value:
+ * 'conditional' string Comments for IE 6, lte IE 7, etc.
+ *
+ * @see WP_Dependency::add_data()
+ *
+ * @since 4.2.0
+ *
+ * @param string $handle Name of the script.
+ * @param string $key    Name of data point for which we're storing a value.
+ * @param mixed  $value  String containing the data to be added.
+ * @return bool True on success, false on failure.
+ */
+function wp_script_add_data( $handle, $key, $value ){
+	global $wp_scripts;
+	return $wp_scripts->add_data( $handle, $key, $value );
+}
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 2232685262..ec940ba6ca 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.2-alpha-31222';
+$wp_version = '4.2-alpha-31223';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.