Challenge 3: Choose Button vs Link — Possible Solution
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(a) A "Log out" control that clears a session and redirects to the
    homepage
    -> BUTTON (with a caveat noted below)

    At first glance this might look like a "link" because it ends in
    navigation (redirecting to the homepage) — but the chapter's
    distinction is about what the control PRIMARILY does and, more
    specifically, whether it performs a meaningful ACTION with a side
    effect beyond simple navigation. Logging out clears session state —
    a real action with consequences, not just "go look at a different
    page." Following this chapter's own examples ("submitting a form,
    toggling state"), an action with a side effect like this is more
    appropriately a <button>, especially since the redirect afterward
    is a CONSEQUENCE of the action, not the action's actual purpose.

    (A common real-world alternative: a <form> containing a <button
    type="submit"> that POSTs to a logout endpoint, which then performs
    a server-side redirect — this avoids using a plain GET link for an
    action with side effects at all, a security-adjacent detail beyond
    this chapter's specific scope but worth flagging as the more robust
    real-world pattern.)

(b) A "Read more" control that expands a hidden paragraph in place,
    without navigating anywhere
    -> BUTTON

    This is a much clearer case: nothing about this control changes the
    URL, loads new content from the server, or moves the user to a
    different page or section — it simply toggles the visibility of
    existing content already on the same page. This matches the
    chapter's button criteria directly: "toggling a menu" is explicitly
    given as an example of button-appropriate behavior, and expanding a
    hidden paragraph in place is functionally identical in kind. Using
    an <a href="#"> here (a common but incorrect pattern) would
    misleadingly suggest to a screen reader user that activating it
    navigates somewhere, when in fact nothing about the page's location
    changes at all.

WHY THIS WORKS AS AN ANSWER
------------------------------
Both cases apply the chapter's core test: does activating this control
primarily perform an ACTION (with or without an eventual navigation as
a side effect), or does it primarily NAVIGATE to different content or a
different location? Case (b) is unambiguous under this test. Case (a)
is a genuinely more nuanced real-world case — which is exactly why it's
worth reasoning through explicitly rather than picking based on
surface appearance (the fact that navigation happens at the end)
alone.