Concepts

Web Apps - Concepts

Manifest, or WebManifest

This refers to the document described by the appmanifest spec, with some extra features described by manifest-incubations. This document describes metadata and developer configuration of an installable web app.

For code representations of the manifest see the list.

Manifest Link

A manifest link is something that looks like this in a html document:

<link rel="manifest" href="manifest.webmanifest">

This link ties the manifest to the document, and subsequently used in the spec algorithms defined in appmanifest or manifest-incubations to describe the webapp and determine if it is installable.

Installable

If a document or page is considered "installable", then the user agent can create some form of installed web app for that page. To be installable, web_app::CanCreateWebApp must return true, where:

• The user profile must allow webapps to be installed
• The web contents of the page must not be crashed
• The last navigation on the web contents must not be an error (like a 404)
• The url must be http, https, or chrome-extension

This is different from promotable below, which determines if Chrome will promote installation of the page.

Promotable

A document is considered "promotable" if it fulfills a set of criteria. This criteria may change to further encourage a better user experience for installable web apps. There are also a few optional checks that depend on the promotability checker. This general criteria as of 2022/09/08:

• The document contains a manifest link.
• The linked manifest can be processed according to the spec and is valid.
• The processed manifest contains the fields:
  • name
  • start_url
  • icons with at least one icon with a valid response that is a parsable image.
  • display field that is not "browser"
• "Serviceworker check": The start_url is 'controlled' (can be served by) a serviceworker with a fetch handler. Optionally turned off
  • Note: This is expected to be removed in Q4 2022.
• "Engagement check": The user has engaged with, or interacted with, the page or origin a certain amount (currently at least one click and some seconds on the site). Optionally turned off

Notes:

• Per spec, the document origin and the start_url origin must match.
• Per spec, the start_url origin does not have to match the manifest_url origin
• The start_url could be different from the document_url.

Manifest id

The id specified in the manifest represents the identity of the web app. The manifest id is processed following the algorithm described in appmanifest specification to produce the app's identity. In the web app system, the app's identifier is hashed to be stored to WebApp->app_id().

If a manifest is discovered during any sort of page load, then the update process is initiated for that manifest. If it resolves to an app_id that is installed, then it will perform an update. See documentation for more information.

Scope

Scope refers to the prefix that a WebApp controls. All paths at or nested inside of a WebApp's scope are thought of as "controlled" or "in-scope" of that WebApp. This is a simple string prefix match. For example, if scope is /my-app, then the following will be "in-scope":

• /my-app/index.html
• /my-app/sub/dir/hello.html
• /my-app-still-prefixed/index.html (Note: if the scope was /, then this would not be out-of-scope)

And the following will be "out-of-scope":

• /my-other-app/index.html
• /index.html

Display Mode

The display of a web app determines how the developer would like the app to look like to the user. See the spec for how the display member is processed in the manifest and what the display modes mean.

Isolated Web Apps

See this document for more information.