From mboxrd@z Thu Jan  1 00:00:00 1970
From: Nicolas Goaziou <mail@nicolasgoaziou.fr>
Subject: Re: CUSTOM_ID vs ID
Date: Sun, 28 Jul 2019 10:10:01 +0200
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In-Reply-To: <CAC=HedBZF-X_2jhhbHOERZMphEtX+UpCgtswHnh8T5RFCYi_sg@mail.gmail.com>
 (Nathan Neff's message of "Sat, 27 Jul 2019 18:35:41 -0500")
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To: Nathan Neff <nathan.neff@gmail.com>
Cc: emacs-orgmode <emacs-orgmode@gnu.org>

Hello,

Nathan Neff <nathan.neff@gmail.com> writes:

> I've often been confused why org-mode has both a CUSTOM_ID
> and a ID property.  I mean, why not just use one or the other name?

Custom ID are user-defined, and only meaningful in the scope of the
document. Also, they may appear as-is when exported, e.g., as an anchor
in HTML.

ID are (or should be) generated by Org, and are valid across files,
which means they need to be absolutely unique.  

Org keeps track of ID if `org-id-track-globally' is non-nil (the
default). If this is nil, there is almost no difference between ID and
custom ID.

> When would I ever have both an ID and a CUSTOM_ID property for
> a heading?

You may want to refer to a heading from anywhere with id:... but need
a clean anchor in HTML export, for example.

FWIW, I never use ID property.

Regards,

-- 
Nicolas Goaziou