Existing Wording: Note that complex extensions are allowed to have elements in the complex extension that are marked is modifier = true, in that the modify the extension value itself. Such elements are conveyed using "extension", not "modifierExtension" because the impact of the modifier element is expected to be known by applications that understand the containing extension. Any modifierExtension defined outside an extension cannot be placed in another extension.

Comment:

This is unclear, but I dont know enough about it to suggest a correction.

Summary:

This is unclear, but I dont know enough about it to suggest a correction.