Tab / TabContainer: Tab expand button (overflow arrow) incorrectly exposed as interactive element to screen readers

Description

In the TabContainer component (used internally by ObjectPage), when a Tab has sub-items and its own content (the "two-click area" pattern), the expand/overflow arrow button is rendered as a fully interactive <ui5-button> element. This causes screen readers (e.g., JAWS in VPC mode) to announce it as a separate "More" menu button and expose it in the Button List.

In the SAPUI5 reference implementation (sap.uxap.ObjectPageLayout), the equivalent overflow arrow icon is treated as decorative — it uses role="presentation" and aria-hidden="true", so only the tab itself is exposed to screen readers.

Affected Component

@ui5/webcomponents — Tab / TabContainer (version 2.24.0)

Reproduction Steps

1. Create an ObjectPage with an ObjectPageSection that contains multiple ObjectPageSubSection children:

<ObjectPage>
  <ObjectPageSection titleText="General Information">
    <ObjectPageSubSection titleText="Details">...</ObjectPageSubSection>
    <ObjectPageSubSection titleText="Description">...</ObjectPageSubSection>
  </ObjectPageSection>
  <ObjectPageSection titleText="Additional Settings">...</ObjectPageSection>
</ObjectPage>

2. Open the page with JAWS screen reader enabled
3. Open the JAWS Button List (INSERT + F7) or navigate in Virtual PC Cursor mode
4. Observe that a "More" button appears as a separate actionable element next to the "General Information" tab

Expected Behavior (SAPUI5 Reference)

The expand/overflow arrow should be decorative only, matching the SAPUI5 sap.uxap.ObjectPageLayout behavior:

<!-- SAPUI5 reference: expand icon is decorative -->
<span role="presentation" aria-hidden="true" aria-label="More"
      class="sapMITBFilterExpandIcon">
</span>

• role="presentation" — not exposed to accessibility tree
• aria-hidden="true" — invisible to screen readers
• No separate focus stop or interactive element
• The tab itself has aria-haspopup="menu" to indicate it opens a submenu

Reference sample: https://ui5.sap.com/#/entity/sap.uxap.ObjectPageSection/sample/sap.uxap.sample.ObjectPageSection

Actual Behavior (UI5 Web Components)

The expand button is rendered as an interactive <ui5-button> in TabInStripTemplate.js:

// When requiresExpandButton === true (two-click area)
<div class="ui5-tab-expand-button">
  <Button
    icon={slimArrowDownIcon}
    design="Transparent"
    tabindex={-1}
    tooltip={this.expandButtonTitle}  // "More"
    accessibilityAttributes={{ hasPopup: "menu" }}
  />
</div>

This causes:

• JAWS announces: "More button menu Press down arrow key to open subitems menu"
• The button appears in the JAWS Button List as a separate actionable item
• Users may be confused about the relationship between the tab and the "More" button

Root Cause

In Tab.js, the requiresExpandButton getter returns true when a tab has sub-items AND its own content:

get requiresExpandButton() {
    return this.items.length > 0 && this._isTopLevelTab && this.hasOwnContent;
}

This triggers the rendering of a full <Button> component instead of a decorative icon.

Suggested Fix

The expand button in the "two-click area" pattern should follow the SAPUI5 reference approach:

1. Replace the interactive <Button> with a non-interactive icon element
2. Add role="presentation" and aria-hidden="true" to the expand icon
3. Keep aria-haspopup="menu" on the parent tab element (already present)
4. The click handler can remain on the icon's container <div> without requiring it to be an accessible button

Environment

• @ui5/webcomponents: 2.24.0
• @ui5/webcomponents-react: 2.24.1
• Screen reader: JAWS (latest)
• Browser: Chrome (latest)

Impact

• Accessibility: Violates WCAG expectations — decorative elements should not be exposed to assistive technology
• Usability: Confuses screen reader users who encounter an unexpected "More" button separate from the tab

Start in TabInStripTemplate.js, where the two-click-area expand control is rendered, and inspect Tab.js for the requiresExpandButton condition. Reproduce the ObjectPage case with a screen reader, then verify that the arrow is decorative and hidden from the accessibility tree while the parent tab retains aria-haspopup="menu".