Do not upcast/downcast root elements (editables).
Introduced widgets.repository#addUpcastCallback method.
Added changelog entry.
Merge branch 't/11186'
Post #11186 simplification and comments.
Don't change type of element#attributes.
Added changelog entry.
Merge branch 't/11307'
Fire 'saveSnapshot' in setData.
Unified the way two callbacks are added in setData.
Introduce editable.status.
Check the status of editable in undo manager.
Do not change snapshots stack when editor is in mode difference than 'wysiwyg'.
Remove if !this.editor.mode, this is checking later.
Add status 'detached' to editable.
Set status 'ready' only if previous status was 'unloaded'.
Fixed mixed spaces with tabs in doc strings.
Sourcearea's status has to be set to ready too.
Set editable status precisely.
Code optimization - better to have one listener only.