The !extend tag may be used to extend an entire YAML file. It would be useful if one could extend a node within the file instead of the entire file.

Reasons

• One might want to extend a portion of a definition, like an area availability, a subapp, or a form tab.

Syntax suggestion:
To extend the image tab from the MTK textImage dialog:
!extend:/mtk/dialogs/components/link.yaml@form.tabs.tabImage

(Or is the @ a bad choice because it implies something else?)