The event is designed to enable listeners to act on specific TypoScript conditions. Listeners must not modify TypoScript at this point, the core will try to actively prevent this.

This event is especially useful when "upper" middlewares that do not have the determined TypoScript need to behave differently depending on TypoScript 'config' that is only created after them. The core uses this in the TimeTrackInitialization and the WorkspacePreview middlewares, to determine debugging and preview details.

Note both 'settings' ("constants") and 'config' are always set within the FrontendTypoScript at this point, even in 'fully cached page' scenarios. 'setup' and (@internal) 'page' may not be set.