ContextQMD
Back to Content

Permissions-Policy: deferred-fetch-minimal directive

files/en-us/web/http/reference/headers/permissions-policy/deferred-fetch-minimal/index.md

latest3.6 KB
Original Source

{{SeeCompatTable}}

The deferred-fetch-minimal {{HTTPHeader("Permissions-Policy")}} directive is part of the Fetch API.

This directive, along with {{HTTPHeader("Permissions-Policy/deferred-fetch", "deferred-fetch")}}, determines how the overall 640KiB quota limit is distributed between the top-level origin and its cross-origin subframes. By default, the top-level origin is granted 512KiB, and each cross-origin subframe is granted 8KiB out of the remaining 128KiB. The deferred-fetch-minimal Permissions Policy can also block all origins; this will reallocate the 128KiB shared limit to the top-level quota, giving it access to the full 640KiB limit.

See fetchLater() quotas for more details and examples.

Syntax

http
Permissions-policy: deferred-fetch-minimal=*
Permissions-policy: deferred-fetch-minimal=()
Permissions-policy: deferred-fetch-minimal=(self)
Permissions-policy: deferred-fetch-minimal=(<url-list>)
  • <url-list>
    • : A space-separated list of origins that are allowed to use the secondary 128KiB quota (with a maximum of 8KiB per subframe).

A top-level frame with the deferred-fetch-minimal permission set to self or () does not allowed the default shared 128kb quota to be used by cross-origin subframes at all. Instead, the 128KiB quota for subframes is added to its normal quota.

Default policy

The default allowlist for deferred-fetch-minimal is *.

Examples

See fetchLater() quotas for more examples.

Using up the minimal quota

http
Permissions-Policy: deferred-fetch=(self "https://b.com")
  1. A subframe of b.com receives 64KiB upon creation, from the top-level's 512KiB limit.
  2. A subframe of c.com is not listed and so receives 8KiB upon creation from the 128KiB shared limit.
  3. 15 more subframes would receive 8KiB upon creation (similar to c.com, and another c.com subframe would also receive another 8KiB quota).
  4. The next subframe would not be granted any quota.
  5. If one of the subframes is removed, its deferred fetches will be sent.
  6. The next subframe would receive an 8KiB quota, as there is quota available again.

Revoking the minimal quota altogether with exceptions

http
Permissions-Policy: deferred-fetch=(self "https://b.com")
Permissions-Policy: deferred-fetch-minimal=()
  1. A subframe of b.com receives 64KiB upon creation.
  2. A subframe of c.com receives no quota upon creation.
  3. The top-level document and its same-origin descendants can use up to the full 640KiB, but that is reduced to 574KiB if a b.com subframe is created.

Revoking the minimal quota altogether with no exceptions

http
Permissions-Policy: deferred-fetch-minimal=()
  1. The top-level document and its same-origin descendants can use up the full 640KiB.
  2. Subframes are not allocated any quota and cannot use fetchLater().

Restricting the minimal quota to named origins

http
Permissions-Policy: deferred-fetch=(self "https://b.com")
Permissions-Policy: deferred-fetch-minimal=("https://c.com")
  1. A subframe of b.com receives 64KiB upon creation.
  2. A subframe of c.com receives 8KiB upon creation.
  3. A subframe of d.com receives no quota upon creation.

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also