feature: Control element is now optional

The control element for `CollapsableItem` is now optional. If there is no control element, you can either expand / collapse the item programmatically from JS, or you can use an external link.

src/CollapsableExtLink.ts

@@ -40,7 +40,7 @@ export class CollapsableExtLink {
 		this.extLink.addEventListener('click', this.listener)
 	}
 
-	public toggleClass(): void {
+	public toggleState(): void {
 		const { options } = this.collapsable
 
 		this.extLink.classList.toggle(options.classNames.externalLinkActive, this.collapsableItem.isExpanded)

src/CollapsableItem.ts

@@ -41,7 +41,7 @@ export class CollapsableItem {
 		const controlElements = element.querySelectorAll<HTMLElement>(collapsable.options.control)
 		const boxElements = element.querySelectorAll<HTMLElement>(collapsable.options.box)
 
-		if (!controlElements.length || !boxElements.length) {
+		if (!boxElements.length) {
 			throw new Error(`Collapsable: Missing control or box element.'`)
 		}
 
@@ -157,7 +157,7 @@ export class CollapsableItem {
 		this._isExpanded = action === 'expand'
 
 		const extLinks = this.collapsable.getExtLinkById(this.id)
-		extLinks.forEach((extLink) => extLink.toggleClass())
+		extLinks.forEach((extLink) => extLink.toggleState())
 
 		this.controlInteractiveElements.forEach((link) => link.setAttribute('aria-expanded', String(action === 'expand')))
 		this.boxElements.forEach((box) => {