docs(header): add comment

Author: thetaPC

core/src/components/header/header.utils.ts

@@ -181,6 +181,15 @@ export const setHeaderActive = (headerIndex: HeaderIndex, active = true) => {
   } else {
     headerEl.classList.add('header-collapse-condense-inactive');
 
+    /**
+     * The small title should only be accessed by screen readers
+     * when the large title collapses into the small title due
+     * to scrolling.
+     *
+     * Originally, the header was given `aria-hidden="true"`
+     * but this caused issues with screen readers not being
+     * able to access any focusable elements within the header.
+     */
     ionTitles.forEach((ionTitle) => {
       if (ionTitle) {
         ionTitle.setAttribute('aria-hidden', 'true');