// Delete the currently-active dfn panel.
    queryAll(".dfn-panel").forEach(dfnPanel=>hideDfnPanel({dfnPanel}));
}

function showDfnPanel(dfn) {
    hideAllDfnPanels(); // Only display one at a time.

    dfn.setAttribute("aria-expanded", "true");

    const dfnPanel = genDfnPanel(dfn, dfn.panelData);

    // Give the dfn a unique tabindex, and then
    // give all the tabbable panel bits successive indexes.
    let tabIndex = 100;
    dfn.tabIndex = tabIndex++;
    const tabbable = dfnPanel.querySelectorA