# Appendix 5.A Prior Art

_Peios / Peios technical reference / PGSS / Applications_

> Where this chapter sits against freedesktop desktop entries and MIME applications, Windows' shortcuts, App Paths, registered applications and default choices, MSIX manifests and the former Atrium catalogue, and which resemblances are deliberate.

## 5.A.1 The freedesktop desktop entry specification

This chapter is, in outline, a desktop entry: one small file per
application, installed by its package into a shared directory, with a
name, an icon, an executable and the MIME types it handles. `title` is
`Name`, `icon` is `Icon`, `opens` is `MimeType`, and `listed = false`
is `NoDisplay=true` without the double negative.

What it drops is `Exec`. A desktop entry's `Exec` is a command line
with its own quoting rules and a set of field codes, `%f`, `%F`, `%u`,
`%U`, `%i`, `%c`, `%k`, that every consumer must parse and expand, and
that have been the source of most of the specification's errata and
several of its security advisories. This chapter has `program`, an
absolute path, and `arguments`, an array that is passed as it is, with
the file last. There is nothing to parse and nothing to expand.

It also drops `Categories`, `Keywords`, `Actions`, `TryExec`,
`Terminal`, `StartupNotify` and the localised forms of every key,
along with `update-desktop-database` and the `mimeinfo.cache` it
builds. A first version needs a title, a program, an icon and the
types it opens, and a directory that is its own index.

## 5.A.2 Windows

Windows has three answers to what an application is, and this chapter
takes something from each. A Start Menu shortcut is a file in a shared
directory whose presence is the listing, which is the shape of §5.4.
`App Paths` in the registry lets a name resolve to an absolute path
without a `PATH` lookup, which is why `program` is absolute. Registered
applications and `Default Programs` let a program say what it opens,
which is `opens`. The default Windows keeps beside it, a machine's in
`HKEY_LOCAL_MACHINE` and a person's own `UserChoice` under
`HKEY_CURRENT_USER`, is the shape of §5.7: a person's choice before the
machine's, each a registry value.

What this chapter does not take is the registry as the place for
declarations. Peios has a registry and does not use it for them,
because a package installs files, and a file is present or it is not:
there is no second thing to keep consistent with the first. A choice is
another kind of thing. It is not installed by a package but made by a
person, it belongs to someone, and who may change it is a question of
access control. Keeping who-may-change-what is what the registry is
for, and `CurrentUser\` gives each person their own place without a
file in their home directory for every consumer to find.

Windows protects `UserChoice` with a hash, so that a program cannot
quietly make itself a person's default. §5.7 does not: a program
running as a person can already do whatever it would have done by
being the default, so the hash protects little that the person's own
token does not already give away. What a choice can never do here is
add a candidate, or run anything a package did not install.

## 5.A.3 freedesktop MIME applications

The freedesktop MIME applications specification keeps defaults in
`mimeapps.list` files, a person's in their configuration directory
before the system's, under `[Default Applications]`, with a list of
applications per type to try in order. §5.7 keeps the order, the
person's before the system's, and takes one application per choice
rather than a list: a choice that is not usable falls through to the
machine's, which is the second entry such a list exists for. It drops
the `[Added Associations]` and `[Removed Associations]` sections, which
let a person make an application a candidate for a type it does not
declare, or stop it being one; here a candidate is what a declaration
says, and nothing a person keeps can change it.

## 5.A.4 MSIX

An MSIX manifest declares an application's entry point, display name
and visual assets in one document the package ships, and the package
manager reads it at install. That is the shape of a declaration, kept
as a file the package installs rather than something the package
manager extracts, so that presence is enough.

## 5.A.5 Atrium

Atrium was Peios' previous web shell and has been completely replaced by
GXWI. Its historical application catalogue influenced this chapter's
"presence is the catalogue" rule: installing a declaration is enough;
nothing registers at install time.

This chapter carries forward TOML declarations and names derived from the
installed file, rather than a separate `id` key. The former Atrium model
loaded a web document from an application directory; PGSS Applications
declares a program to run and an icon name for PGSS Icons to resolve.

## 5.A.6 Design influences

**A declaration, not a place.** An application is what a file says it
is, and not where a binary sits. A program can be a command and an
application at once, a wrapper or a script can be an application, and
nothing about a program's path has to change for it to become one.

**Matched by file, named by path.** A running process is matched to its
declaration by the file it runs, and never by its name, so that no
program can borrow another's title by being called the same thing. A
declaration names its program absolutely for the same reason.

**Data, never a command line.** The one thing every consumer does with
a declaration is start a process from it, often because something
untrustworthy asked. Passing the program and arguments through exactly
as installed is what makes that safe, and is why there are no
placeholders, no shell and no lookup.

**One directory that is its own index.** As with PGSS Icons' themes,
the flat directory is chosen so that no state has to be built,
rebuilt or kept consistent, and so that a package's install and remove
are the whole of the provider's work.

**A choice selects; it never adds.** What may open a file is what
declarations say, and a person's or the machine's choice only says
which of those comes first. A choice that no longer fits is passed
over rather than repaired, so that removing an application, or a
package changing what it opens, needs nobody to tidy the registry
after it.