UI sounds

Folio reports four moments and plays nothing: one handler gives every menu your game's own sounds.

void UMyAudioSubsystem::Initialize(FSubsystemCollectionBase&)
{
	FFolioModule::Get().OnUiSound().AddUObject(this, &UMyAudioSubsystem::PlayUiSound);
}

void UMyAudioSubsystem::PlayUiSound(const Folio::EUiSound Sound)
{
	switch (Sound)
	{
	case Folio::EUiSound::Focus:   Play(FocusCue);   break;
	case Folio::EUiSound::Confirm: Play(ConfirmCue); break;
	case Folio::EUiSound::Back:    Play(BackCue);    break;
	case Folio::EUiSound::Invalid: Play(InvalidCue); break;
	}
}

A revealing <text> reports through its own delegate, because the document names the sound:

void UMyAudioSubsystem::Initialize(FSubsystemCollectionBase&)
{
	FFolioModule::Get().OnTextRevealSound().AddUObject(this, &UMyAudioSubsystem::PlayNamedSound);
}

It fires at most once a frame however fast the text types. See rich text.

Invalid is the one worth taking seriously

Invalid is a click on something disabled (a locked option, a button not available yet). Without a distinct noise a player cannot tell "I missed" from "that is not allowed", and the UI reads as unreliable.

It fires for anything carrying .is-disabled, the component library's class. See input and navigation for the full disabled recipe: a class for the look, focus: none to leave navigation, pointer-events: none to stop responding.

What it does not cover

Anything specific to a screen. A weapon-select sound, a purchase confirmation, a page turn: those belong to the screen. Listen for the element's own events instead:

Element->AddEventListener("click", Listener);

or bind them through a data model. See calling into game code.

Focus on load. A document that opens with autofocus moves focus, which fires Focus. If a menu opening should be silent, gate the first broadcast after a screen change in your handler: Folio does not know a screen change happened.

Where to go next

• Input and navigation: what produces each of the four moments.
• Calling into game code: per-element events, for anything a screen owns.