I was not aware of any implied hierarchy with tags. The order is not important as far as I know, and what you describe as mix-and-match seems ok. There is an idea of inheritance, e.g. sub-headings can inherit tags from higher headings.

In any case, you should be able to use agenda queries to find headings that are lisp and not emacs, lisp+orgmode, etc. 

I am not sure about the org-mode tag. In the past, emacs splits that into :org:mode: for me.

What do you want to do with the tags? 

John

-----------------------------------
Professor John Kitchin 
Doherty Hall A207F
Department of Chemical Engineering
Carnegie Mellon University
Pittsburgh, PA 15213
412-268-7803

On Thu, Feb 1, 2018 at 7:07 AM, Lawrence Bottorff <borgauf@gmail.com> wrote:
Is it possible to have two or more tags that are "peers," i.e., all equal, not in a hierarchy, be in an ad-hoc, as-needed way be hierarchical? For example, I have the tags org-mode, lisp, and emacs, and I want to have a header with the tags

* my header    :emacs:org-mode:lisp:

So the above should be an ad-hoc hierarchy of

- emacs
   - org-mode
      - lisp

As I understand, the order indicates the level in a hierarchy. True? So the above has emacs at the top of the tag hierarchy, then org-mode, then lisp. Correct? So yes, I could simply set up this hierarchy. But what I really want is to not have these tags in any set hierarchy, rather, be able to use them independently, mix-and-match, e.g., 

* Another Header    :emacs:lisp:

or maybe

* Yet Another Header   :lisp:

and this would be just about non-Emacs, non-org-mode Lisp. Is this mix-and-match possible?

LB