Challenge 1: Map Techniques to POUR — Possible Solution
====================================================================

(a) Adding alt text to images
    -> PERCEIVABLE

    Alt text exists specifically so that content which is normally
    conveyed VISUALLY (an image) can still be PERCEIVED by someone who
    can't see it — a screen reader reads the alt text aloud instead of
    the image itself. This is a direct, textbook example of making
    content "presentable in ways every user can perceive," exactly the
    chapter's definition of Perceivable.

(b) Ensuring a modal can be closed with the Escape key
    -> OPERABLE

    This is entirely about whether an interface component can actually
    be USED — specifically, whether a keyboard-only user (someone who
    can't click an X button with a mouse) has a way to interact with
    and dismiss the modal. The chapter defines Operable as "usable by
    everyone," including "full keyboard support" — Escape-to-close is a
    concrete instance of exactly that requirement.

(c) Writing clear, jargon-free error messages
    -> UNDERSTANDABLE

    This is about whether the MEANING of the content is comprehensible
    once someone can perceive it and interact with it — an error
    message using confusing jargon might be technically readable (by a
    screen reader) and technically reachable (via keyboard), but still
    fail to actually communicate what went wrong or what to do next.
    The chapter's Understandable principle covers exactly this:
    "content and operation must be comprehensible."

WHY THIS WORKS AS AN ANALYSIS
--------------------------------
Each of the four POUR principles addresses a DIFFERENT stage of a
user's interaction with content: can they PERCEIVE it exists at all
(Perceivable), can they OPERATE whatever control it presents (Operable),
and once they've perceived and operated it, do they UNDERSTAND what it
means or what happened (Understandable) — with Robust sitting slightly
apart, concerned with whether the underlying markup itself holds up
across different assistive technologies rather than being about a
specific user interaction. Recognizing which STAGE a given technique
addresses is the key to correctly mapping it to one of the four
pillars.