"<code>default</code>", "<code>prompt</code>"».

<pclass="note">The "<code>default</code>" type represents a fallback

when no specific handler is defined for a given prompt type. The

"<code>beforeUnload</code>" prompt type does not use this default

handler, but instead falls back to the "<code>accept</code>" handler

if no more specific handler is defined. This is because HTTP-only

sessions do not allow the "<code>beforeUnload</code>" handler to be

customized, and enabling other protocols isn&apos;t expected to change

the user prompt handling as a side effect.

when no specific handler is defined for a given prompt type, including

the "<code>beforeUnload</code>" prompt type. It can only be set if the

unhandled prompt behavior is a<adata-cite=infra>map</a> which

[=map/contains=] "<code>default</code>". For HTTP-only sessions setting

unhandled prompt behavior as a string value, the value will be assigned to

the internal type "<code>fallbackDefault</code>". The

"<code>fallbackDefault</code>" value is not used for the

"<code>beforeUnload</code>" prompt type, instead it falls back to the

"<code>accept</code>" handler. This is because HTTP-only sessions do not

allow the "<code>beforeUnload</code>" handler to be customized, and enabling

other protocols isn&apos;t expected to change the user prompt handling as a

side effect.

<p>To<dfn>deserialize as an unhandled prompt behavior</dfn> given

argument<var>value</var>:

and [=prompt handler configuration/notify=] false.

<li><p>If<var>handlers</var> contains "<code>fallbackDefault</code>"

return<var>handlers</var>["<code>default</code>"].

return<var>handlers</var>["<code>fallbackDefault</code>"].

<li><p>Return a<a>prompt handler

configuration</a> with [=prompt handler