&$parser: Parser object
&$ig: ImageGallery object
+'BitmapHandlerTransform': before a file is transformed, gives extension the
+possibility to transform it themselves
+$handler: BitmapHandler
+$image: File
+&$scalerParams: Array with scaler parameters
+&$mto: null, set to a MediaTransformOutput
+
'BlockIp': before an IP address or user is blocked
$block: the Block object about to be saved
$user: the user _doing_ the block (not the one being blocked)
$target: Title/string of redirect target
$article: Article object
+'InterwikiLoadPrefix': When resolving if a given prefix is an interwiki or not.
+Return true without providing an interwiki to continue interwiki search.
+$prefix: interwiki prefix we are looking for.
+&$iwData: output array describing the interwiki with keys iw_url, iw_local,
+ iw_trans and optionally iw_api and iw_wikiid.
+
'InternalParseBeforeLinks': during Parser's internalParse method before links
but after noinclude/includeonly/onlyinclude and other processing.
&$parser: Parser object
$ip: IP of the user who sent the message out
$u: the account whose new password will be set
+'UserAddGroup': called when adding a group; return false to override
+stock group addition.
+$user: the user object that is to have a group added
+&$group: the group to add, can be modified
+
'UserArrayFromResult': called when creating an UserArray object from a
database result
&$userArray: set this to an object to override the default object returned
$inject_html: Any HTML to inject after the "logged out" message.
$oldName: name of the user before logout (string)
+'UserRemoveGroup': called when removing a group; return false to override
+stock group removal.
+$user: the user object that is to have a group removed
+&$group: the group to be removed, can be modified
+
'UserRights': After a user's group memberships are changed
$user : User object that was changed
$add : Array of strings corresponding to groups added