A wiki can be made readonly like so:
$wgReadOnly = true;
If the editor has been opened before read only mode has been invoked, and an edit is completed with the **mobile source editor**, when the save fails, a toast is presented with a generic error message, but the toast is not visible until you scroll down, and the toast appears "underneath" the article content. The error message should probably display the "apierror-readonly" message [EditorOverlay.js#L285](https://github.com/wikimedia/mediawiki-extensions-MobileFrontend/blob/f4c03a10ce202eb70b7b4efd1fe62f58d2c057b0/resources/mobile.editor.overlay/EditorOverlay.js#L285)
= Acceptance criteria
 Make sure any error is displayed inside the editor itself, above the preview, using errorbox class (note other box styles may be inside mobile.special.styles.
 Remove code relating to toast error handling.
 Include and display the apierror-readonly error message when this error occurs
= Developer/designer notes
Code lives inside MobileFrontend.