MediaWiki supports creating pages with preloaded text. This is implemented using the following query parameters:
- preloadtitle: when adding a new section via action=edit§ion=new, it preloads the title of the message
- preload: preloads the contents of the textbox with a wikitext that comes from a certain on-wiki page
The preload query parameter, however, fails to read content of a system message. This makes it harder to make use of preloading from a MediaWiki extension, where content can be provided through an i18n message (and community can easily customize it as needed by making an on-wiki edit).
EditPage class checks for Title::exists, while for this use-case, calling either Title::hasSourceText or Title::isKnown sounds more reasonable. Switching would require changing WikiPage::getContent to something that can get texts of both system messages and database-recorded pages.