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/// The document event the scroll spy polls on.
///
/// Deliberately a `setInterval` rather than a `scroll` listener or
/// `requestAnimationFrame`: the app shell locks the viewport and scrolls
/// an inner container, and a delegated `scroll` listener on `document`
/// can stay silent while that container scrolls, while rAF is paused
/// outright in a hidden tab. A short interval reads one property per
/// tick and early-outs when nothing moved, so it costs effectively
/// nothing and behaves the same in a background tab.
pub const TOC_SPY_INTERVAL_MILLIS: i32 = 100;
/// How far below the top of the scroll container a heading has to sit
/// before it counts as the active section, in CSS pixels.
///
/// Matches the visual reading line: a heading a little scrolled past the
/// top edge has already been read, so the next one lights up. A heading
/// still hidden above the edge does not.
pub const TOC_SPY_READING_LINE_PX: f64 = 100.0;
/// Tolerance in CSS pixels for treating the container as scrolled to its
/// end, where the last heading should win rather than the first one that
/// is technically still on screen.
pub const TOC_SPY_END_TOLERANCE_PX: f64 = 4.0;
/// Selector of the scrollable prose column the spy measures against.
///
/// This must name the element that actually scrolls. The shell locks
/// the viewport (`html, body { overflow: hidden }`) and scrolls
/// `.c_app_main`, which is the only element carrying `overflow-y: auto`.
/// `.c_euv_doc_content` is the prose *layout* wrapper: it is a flex column
/// with `overflow: visible` whose `scrollHeight` equals its
/// `clientHeight` on every page, so measuring it made the "scrolled to
/// the end" test permanently true and pinned the highlight to the last
/// TOC entry no matter where the reader scrolled to.
pub const TOC_SPY_CONTAINER_SELECTOR: &str = ".c_app_main";
/// Selector matching every TOC anchor, flat or nested.
pub const TOC_SPY_LINK_SELECTOR: &str = ".c_euv_doc_toc a, .c_euv_toc a";
/// The `href` attribute read from each TOC anchor.
pub const HREF_ATTR: &str = "href";