Challenge 2: Choose Polite or Assertive — Possible Solution
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(a) "Your changes have been saved" after a routine form edit
    -> aria-live="polite" (or role="status")

    This is a ROUTINE confirmation, not something requiring the user's
    immediate attention — the chapter's tip box specifically calls out
    exactly this kind of message ("a 'form saved' confirmation") as a
    case where reaching for assertive is tempting but wrong. The user
    doesn't need to be interrupted mid-action to hear this; it can wait
    for a natural pause in whatever the screen reader is currently
    doing, which is precisely what "polite" means. Using assertive here
    would disrupt the user's flow for information that carries no real
    urgency.

(b) "Your session is about to expire in 10 seconds"
    -> aria-live="assertive" (or role="alert")

    This IS genuinely urgent and time-sensitive — the chapter's own
    table describes assertive as reserved for "genuinely urgent
    information," and a session-expiration warning with only a 10-second
    window is a strong example of that. If this were announced
    "politely" (waiting for a natural pause), a screen reader user
    could easily miss it entirely or hear it too late to act — for
    instance, if they're in the middle of reading a long page and the
    polite announcement gets queued behind everything else, several of
    those 10 seconds could elapse before they even hear the warning.
    The disruption of interrupting them is justified here specifically
    because the cost of NOT interrupting (losing their session with no
    warning) is worse than the disruption itself.

WHY THIS WORKS AS A DECISION FRAMEWORK
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The deciding question in both cases is the same: "does the COST of
interrupting the user right now outweigh the cost of them possibly
missing or delaying hearing this information?" For (a), interrupting
costs more than it gains — nothing bad happens if the user hears "saved"
a moment later than expected. For (b), NOT interrupting costs more —
missing a time-limited warning has a real, negative consequence
(getting logged out unexpectedly). This mirrors the chapter's overall
guidance directly: assertive is for the rare cases where interruption
is actually the lesser harm, not the default choice for anything that
merely feels important.