I'll try to explain my view of tags. Let's see if it makes sense. :)
Conceptually, properties are like a generic key-value store for
headings, and tags are like a certain property. Imagine if, instead of
tags being placed in headings, like this:
* Blueberries :food:fruit:
...tags were implemented as properties, like this:
* Blueberries
:PROPERTIES:
:TAGS: food fruit
:END:
The meaning would be essentially the same.
>From a technical perspective, putting tags on headings makes them much
faster to search for, because a regexp can be used to search directly to
them (local ones, anyway). In contrast, to find the next location of a
certain property, a single regexp search is not enough, because even if
a regexp search was done to find an entry like the previous example,
like:
(re-search-forward
(rx bol ":TAGS:" (1+ blank) (0+ nonl) bow "food" eow)
nil t)
...it would not be guaranteed that the result would actually be in a
heading's property drawer, so additional checks must be done to ensure
that.
Some properties are special, like CATEGORY. As well, some properties
are "virtual," like SCHEDULED, which is written like:
* Heading
SCHEDULED: <2019-12-20 Fri 11:00>
...but is accessible with org-entry-get, like a property in a drawer.
So, use tags for applying simple, conceptual labels to headings, because
they're faster to search for than properties and always visible. Use
properties as a key-value store for details that are less likely to be
used in a query and are less important to see.
What do you think? :)
