Index: includes/parser/Parser.php
===================================================================
--- includes/parser/Parser.php	(revision 108087)
+++ includes/parser/Parser.php	(working copy)
@@ -100,6 +100,7 @@
 
 	# Persistent:
 	var $mTagHooks = array();
+	var $mTagPSTHooks = array();
 	var $mTransparentTagHooks = array();
 	var $mFunctionHooks = array();
 	var $mFunctionSynonyms = array( 0 => array(), 1 => array() );
@@ -3727,6 +3728,25 @@
 				extract( $flags );
 			}
 		} else {
+
+			if ( $this->ot['wiki'] ) {
+				//we're in preSaveTransform, allow the tag extension to transform its contents
+				$lcname = strtolower( $name );
+				$attributes = Sanitizer::decodeTagAttributes( $attrText );
+				if ( isset( $params['attributes'] ) ) {
+					$attributes = $attributes + $params['attributes'];
+				}
+
+				if ( isset( $this->mTagPSTHooks[$lcname] ) ) {
+					# Workaround for PHP bug 35229 and similar
+					if ( !is_callable( $this->mTagPSTHooks[$lcname] ) ) {
+						throw new MWException( "Tag PST hook for $lcname is not callable\n" );
+					}
+					$content = call_user_func_array( $this->mTagPSTHooks[$lcname],
+						array( $content, $attributes, $this, $frame ) );
+				}
+			}
+
 			if ( is_null( $attrText ) ) {
 				$attrText = '';
 			}
@@ -4583,6 +4603,26 @@
 		return $oldVal;
 	}
 
+/**
+	 * As setHook(), but the callback set here will be called during preSaveTransform
+	 * This allows extension tags to do pre-save transformations on their input,
+	 *
+	 * @param $tag Mixed: the tag to use, e.g. 'hook' for <hook>
+	 * @param $callback Mixed: the callback function (and object) to use for the tag
+	 * @return The old value of the mTagPSTHooks array associated with the hook
+	 */
+	public function setPSTHook( $tag, $callback ) {
+		$tag = strtolower( $tag );
+		if ( preg_match( '/[<>\r\n]/', $tag, $m ) ) throw new MWException( "Invalid character {$m[0]} in setPSTHook('$tag', ...) call" );
+		$oldVal = isset( $this->mTagPSTHooks[$tag] ) ? $this->mTagPSTHooks[$tag] : null;
+		$this->mTagPSTHooks[$tag] = $callback;
+		if ( !in_array( $tag, $this->mStripList ) ) {
+			$this->mStripList[] = $tag;
+		}
+
+		return $oldVal;
+	}
+
 	/**
 	 * As setHook(), but letting the contents be parsed.
 	 *
@@ -4614,6 +4654,7 @@
 	function clearTagHooks() {
 		$this->mTagHooks = array();
 		$this->mFunctionTagHooks = array();
+		$this->mTagPSTHooks = array();
 		$this->mStripList = $this->mDefaultStripList;
 	}
 
@@ -5155,7 +5196,8 @@
 	 * @return array
 	 */
 	function getTags() {
-		return array_merge( array_keys( $this->mTransparentTagHooks ), array_keys( $this->mTagHooks ), array_keys( $this->mFunctionTagHooks ) );
+		return array_unique( array_merge( array_keys( $this->mTransparentTagHooks ), array_keys( $this->mTagHooks ), 
+			array_keys( $this->mFunctionTagHooks ), array_keys( $this->mTagPSTHooks ) ) );
 	}
 
 	/**
Index: includes/parser/CoreTagHooks.php
===================================================================
--- includes/parser/CoreTagHooks.php	(revision 108087)
+++ includes/parser/CoreTagHooks.php	(working copy)
@@ -19,6 +19,7 @@
 		$parser->setHook( 'pre', array( __CLASS__, 'pre' ) );
 		$parser->setHook( 'nowiki', array( __CLASS__, 'nowiki' ) );
 		$parser->setHook( 'gallery', array( __CLASS__, 'gallery' ) );
+		$parser->setPSTHook( 'gallery', array( __CLASS__, 'galleryPST' ) );
 		if ( $wgRawHtml ) {
 			$parser->setHook( 'html', array( __CLASS__, 'html' ) );
 		}
@@ -102,4 +103,41 @@
 	static function gallery( $content, $attributes, $parser ) {
 		return $parser->renderImageGallery( $content, $attributes );
 	}
+
+	/**
+	 * Core parser tag preSaveTransform hook function for 'gallery'.
+	 *
+	 * This function applies preSaveTransform to the image descriptions.
+	 *
+	 * @param string $content
+	 * @param array $attributes
+	 * @param Parser $parser
+	 * @return string wikitext
+	 */
+	static function galleryPST( $content, $attributes, $parser ) {
+
+		$lines = StringUtils::explode( "\n", $content );
+		$transformed = array();
+		foreach ( $lines as $line ) {
+			# match lines like these:
+			# Image:someimage.jpg|This is some image
+			$matches = array();
+			preg_match( "/^([^|]+)(\\|(.*))?$/", $line, $matches );
+			# Skip empty lines
+			if ( count( $matches ) == 0 ) {
+				$transformed[] = $line;
+				continue;
+			}
+
+			if ( isset( $matches[3] ) ) {
+				//pre-save transform the second match, which is wikitext
+				$presaved = $parser->preSaveTransform( $matches[2], $parser->getTitle(), $parser->getOptions()->getUser(), $parser->getOptions(), false );
+				$transformed[] = $matches[1] . $presaved;// $matches[2];
+			} else {
+				$transformed[] = $line;
+			}
+
+		}
+		return implode( "\n", $transformed );
+	}
 }