Reference: Feature Flags 

Quick lookup. For per-flag descriptions and usage see Configuration.

Active in 5.x 

Flag Effect
headless.storageProxy Route processed file URLs through frontendFileApi.
headless.elementBodyResponse On POST/PUT/DELETE, return just the element matching responseElementId from the body.
`headless.overrideFluidTemplates Swap ViewFactoryInterface for HeadlessViewFactory. Required to render raw-PHP templates per view.
headless.cookieDomainPerSite Per-site cookieDomain injection middleware.
headless.assetsCacheBusting Append ?<mtime> to processed-file URLs.
headless.prettyPrint JSON_PRETTY_PRINT on every encoder output.

Availability by version 

Flag

2.x

3.x

4.x

5.x

FrontendBaseUrlInPagePreview

available

removed

removed

removed

headless.frontendUrls

>= 2.5

available

removed

removed

headless.storageProxy

>= 2.4

available

available

available

headless.redirectMiddlewares

>= 2.5

available

available

removed (auto-on when EXT:redirects is installed)

headless.nextMajor

>= 2.2

currently not used

currently not used

removed

headless.elementBodyResponse

>= 2.6

available

available

available

headless.simplifiedLinkTarget

>= 2.6

removed

not available

not available

headless.jsonViewModule

not available

>= 3.0

>= 3.0

removed (module discontinued)

headless.workspaces

not available

>= 3.1

removed (auto-on with EXT:workspaces)

removed (works without a flag)

headless.pageTitleProviders

not available

not available

>= 4.2.3 <= 4.4

removed

headless.overrideFluidTemplates

not available

not available

available

available (reworked, see UPGRADE.md)

headless.cookieDomainPerSite

not available

not available

available

available

headless.assetsCacheBusting

not available

not available

available

available

headless.prettyPrint

not available

not available

available

available