This repository is where GitHub looks for organization defaults. A file here is used by any repository that does not have its own copy, so a change to one takes effect immediately across every repository that was relying on it.
Two kinds of file live here. Some are inherited: GitHub hands them to a
repository that has none of its own. The rest, under docs/, are read rather
than inherited — a repository links to them, and they reach nothing by
themselves.
Add a default on its own, not alongside another. Each one reaches a different set of repositories, and that set is what needs checking before the next lands.
This file does not say which repositories those are, or how many. Any count written here is true on the day it is written and silently wrong afterwards, and nobody re-checks a sentence that reads like background. The API answers it per repository, on demand, correctly.
Inheritance is all-or-nothing per file. A repository that has its own copy ignores the default entirely rather than merging with it.
Issue templates are not here. The same all-or-nothing rule covers the whole
ISSUE_TEMPLATE directory, so a central set reaches only repositories that
define none of their own.
Links inside these files: a default file that points at another file in this repository can use a relative path, because that is where it is served from. A pull request template is different — it is inserted into a pull request body in the other repository, so a relative path there would resolve against that repository. Links in a template must be absolute, or absent.
Anything that is safe to publish, safe to change under a repository's feet, and true whatever the repository builds — a service, a library, a site, a game, or infrastructure.
Private repository names, server addresses, deployment topology, internal procedures, secrets or sensitive identifiers, local paths, and anything that would be wrong for one of the kinds of project above.
Rules that are risky to change centrally — a merge method, a runtime version, a verification command — belong to the repository that has to live with them.