feat(ui5-panel): enable configuring the heading level (#1504)

**Background**
Our native title used to be "h1", which is indeed wrong. In openui5 it is "h2" and it is not configurable. But, in the related issue the author wants to be able to change the title level in general. Although we provide the possibility of a custom header, the author is asking for this feature to make use of the fact that the the entire native header is clickable and focusable, which is not the case with the custom one.
**Options**
So, we either reject this and (1) hardcode it to "h2" as in openui5, (2) introduce a property as in this change, or (3) make another slot for the title, but then we will have the current "header" slot and "headerTitle" slot and it might be confusing.
**In this change:**
- [refactoring] Use div with role="heading" and "aria-level" attrs, instead of "h" tag to  enable the configuration of the level. Reuse the existing TitleLevel enum ("H1" to "H6") and extract the number part, but AriaLevel type ("1" - "6") is also an option.
- [FIX] sync the parameters in the latest visual design and change few variables
- [FIX] title now truncates, previously it used to wrap.

Fixes: #1495

packages/main/src/Panel.hbs

@@ -30,8 +30,12 @@
 		{{#if _hasHeader}}
 			<slot name="header"></slot>
 		{{else}}
-			<div class="ui5-panel-header-content">
-				<h1 class="ui5-panel-header-title">{{headerText}}</h1>
+			<div
+				role="heading"
+				aria-level="{{headerAriaLevel}}"
+				class="ui5-panel-header-title"
+			>
+				{{headerText}}
 			</div>
 		{{/if}}
 	</div>

packages/main/src/Panel.js

@@ -8,6 +8,7 @@ import { getAnimationMode } from "@ui5/webcomponents-base/dist/config/AnimationM
 import { fetchI18nBundle, getI18nBundle } from "@ui5/webcomponents-base/dist/i18nBundle.js";
 import "@ui5/webcomponents-icons/dist/icons/navigation-right-arrow.js";
 import Button from "./Button.js";
+import TitleLevel from "./types/TitleLevel.js";
 import PanelAccessibleRole from "./types/PanelAccessibleRole.js";
 import PanelTemplate from "./generated/templates/PanelTemplate.lit.js";
 
@@ -102,6 +103,20 @@ const metadata = {
 			defaultValue: PanelAccessibleRole.Form,
 		},
 
+		/**
+		 * Defines the "aria-level" of <code>ui5-panel</code> heading,
+		 * set by the <code>headerText</code>.
+		 * <br><br>
+		 * Available options are: <code>"H6"</code> to <code>"H1"</code>.
+		 * @type {TitleLevel}
+		 * @defaultvalue "H2"
+		 * @public
+		*/
+		headerLevel: {
+			type: TitleLevel,
+			defaultValue: TitleLevel.H2,
+		},
+
 		/**
 		 * @private
 		 */
@@ -347,6 +362,10 @@ class Panel extends UI5Element {
 		};
 	}
 
+	get headerAriaLevel() {
+		return this.headerLevel.slice(1);
+	}
+
 	get headerTabIndex() {
 		return (this.header.length || this.fixed) ? "-1" : "0";
 	}

packages/main/src/themes/Panel.css

@@ -54,9 +54,17 @@
 	transform: rotate(90deg);
 }
 
+:host([fixed]) .ui5-panel-header-title {
+	width: 100%;
+}
+
 .ui5-panel-header-title {
-	font-family: var(--sapFontFamily);
-	font-size: var(--_ui5_panel_header_title_size);
+	width: calc(100% - var(--_ui5_panel_button_root_width));
+	overflow: hidden;
+	text-overflow: ellipsis;
+	white-space: nowrap;
+	font-family: var(--sapFontHeaderFamily);
+	font-size: var(--sapFontHeader5Size);
 	font-weight: normal;
 	color: var(--sapGroup_TitleTextColor);
 }

packages/main/src/themes/base/Panel-parameters.css

@@ -1,6 +1,5 @@
 :root {
 	--_ui5_panel_focus_border: 1px dotted var(--sapContent_FocusColor);
 	--_ui5_panel_header_height: 3rem;
-	--_ui5_panel_header_title_size: var(--sapMFontHeader4Size);
 	--_ui5_panel_button_root_width: 3rem;
 }

packages/main/src/themes/sap_fiori_3/Panel-parameters.css

@@ -2,6 +2,5 @@
 
 :root {
 	--_ui5_panel_header_height: 2.75rem;
-	--_ui5_panel_header_title_size: var(--sapMFontHeader5Size);
 	--_ui5_panel_button_root_width: 2.75rem;
 }

packages/main/src/themes/sap_fiori_3_dark/Panel-parameters.css

@@ -2,6 +2,5 @@
 
 :root {
 	--_ui5_panel_header_height: 2.75rem;
-	--_ui5_panel_header_title_size: var(--sapMFontHeader5Size);
 	--_ui5_panel_button_root_width: 2.75rem;
 }

packages/main/test/pages/Panel.html

@@ -104,7 +104,7 @@
 
 	<br>
 
-	<ui5-panel id="panel-expandable" accessible-role="Complementary" header-text="Both expandable and expanded">
+	<ui5-panel id="panel-expandable" accessible-role="Complementary" header-text="Both expandable and expanded" header-level="H4">
 
 
 		<!-- Content -->
@@ -160,7 +160,7 @@
 
 	<br>
 
-	<ui5-panel id="panel1" collapsed header-text="Click to expand!">
+	<ui5-panel id="panel1" collapsed header-text="Click to expand!" header-level="H3">
 
 		<!-- Content -->
 		<ui5-title>This is a demo how to use the &quot;expand&quot; event.</ui5-title>

packages/main/test/specs/Panel.spec.js

@@ -101,6 +101,7 @@ describe("Panel general interaction", () => {
 
 		it("tests whether aria attributes are set correctly with native header", () => {
 			const header = browser.$("#panel1").shadow$(".ui5-panel-header");
+			const title = browser.$("#panel1").shadow$(".ui5-panel-header-title");
 			const button = browser.$("#panel1").shadow$(".ui5-panel-header-button");
 
 			assert.ok(!button.getAttribute("aria-expanded"), "aria-expanded shouldn't be set on the button");
@@ -109,6 +110,8 @@ describe("Panel general interaction", () => {
 
 			assert.ok(header.getAttribute("aria-expanded"), "aria-expanded should be set on the header");
 			assert.ok(header.getAttribute("aria-controls"), "aria-controls should be set on the header");
+
+			assert.strictEqual(title.getAttribute("aria-level"), "3", "title aria-level is set to 3 correctly");
 		});
 
 		it("tests whether aria attributes are set correctly in case of custom header", () => {