Index: ApiBase.php
===================================================================
--- ApiBase.php	(revision 72239)
+++ ApiBase.php	(working copy)
@@ -333,7 +333,15 @@
 								$choices[] =  $t;
 							}
 						}
-						$desc .= $paramPrefix . $nothingPrompt . $prompt . implode( ', ', $choices );
+						$desc .= $paramPrefix . $nothingPrompt . $prompt;
+						if ( count( $choices ) > 10 ) {
+							$desc .= "\n";
+							foreach( $choices as $choice ) {
+								$desc .= sprintf( "  %-18s %s\n", "", $choice );
+							}
+						} else {
+							$desc .= implode( ', ', $choices );
+						}
 					} else {
 						switch ( $type ) {
 							case 'namespace':