This is the definition of org-attach-use-inheritance:
(defcustom org-attach-use-inheritance 'selective
"Attachment inheritance for the outline.
Enabling inheritance for org-attach implies two things. First,
that attachment links will look through all parent headings until
it finds the linked attachment. Second, that running org-attach
inside a node without attachments will make org-attach operate on
the first parent heading it finds with an attachment.
Selective means to respect the inheritance setting in
`org-use-property-inheritance'."
:group 'org-attach
:type '(choice
(const :tag "Don't use inheritance" nil)
(const :tag "Inherit parent node attachments" t)
(const :tag "Respect org-use-property-inheritance" selective))
:type 'boolean)
As you can see, it can be either nil, t, or selective. However due to the
:type 'boolean)
line, it's impossible to set it to selective using customize-variable.
Emacs : GNU Emacs 26.1 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.5)
of 2019-09-23, modified by Debian
Package: Org mode version 9.3.6 (9.3.6-elpa @
/home/username/.emacs.d/elpa/org-9.3.6/)
