Message groups bring together a collection of messages. They come with a description and dictate the namespace where messages are stored, how can they be exported (usually via FFS), how are the definitions loaded (like from wiki pages, or via FFS) and other things.
Message group hierarchy
- SvgMessageGroup !!
- WikiPageMessageGroup !!!
! MessageGroupBase is the more recent base class. These groups are usually defined via the Yaml configuration, while the ones extending MessageGroupOld are defined in other ways. Core*MessageGroup are for MediaWiki and are waiting to be migrated to FileBasedMessageGroup.
!! In TranslateSvg extension.
!!! Provides the page translation feature.
Basic info. Each message group has an unique (within a wiki) id, a label (short name) and a short description, that includes important information like licensing and a link to a page which has more information.
Namespace. All the definitions of messages and translations are placed in a namespace specified by the message group. The file based message groups allow users to set the namespace, while the others are hard coded to NS_TRANSLATIONS (page translation) or NS_MEDIAWIKI.
Checkers. Message groups can give a list of message checkers, that can warn the user in case of errors in translation. Common checks are for missing or unknown variables and invalid html.
Mangler. Each group has a message key mangler. It is mostly relevant only to file based message groups where the format of the message keys cannot be enforced. See the mangler section below.
Message loading. There are many methods for loading message definitions. The load method usually reads the messages from files via FFS class or from a database table. getDefinitions is a shortcut for loading the messages in the source language (see below).
Source language. All of the message definitions are expected to be in a single language. Only dynamic message groups like RecentMessageGroup can work around this limitation.
Tags. Messages can have tags. Tags ignored and optional are often used. In addition, message collection provides its own additional tags.
Workflow states. Message groups can override the global workflow states.
Languages. By default all known languages accept translations. The message groups can provide a subset of languages to disable translation in the others.