fix(dom): use case-insensitive match for `is()`

src/dom/htmlelement.spec.ts

@@ -394,6 +394,16 @@ describe("HtmlElement", () => {
 			expect(el.is("bar")).toBeFalsy();
 		});
 
+		it("should match case-insensitive", () => {
+			expect.assertions(4);
+			const a = new HtmlElement("foo");
+			const b = new HtmlElement("BAR");
+			expect(a.is("foo")).toBeTruthy();
+			expect(a.is("FOO")).toBeTruthy();
+			expect(b.is("bar")).toBeTruthy();
+			expect(b.is("BAR")).toBeTruthy();
+		});
+
 		it("should match any tag when using asterisk", () => {
 			const el = new HtmlElement("foo");
 			expect(el.is("*")).toBeTruthy();

src/dom/htmlelement.ts

@@ -140,7 +140,12 @@ export class HtmlElement extends DOMNode {
 	 * If passing "*" this test will pass if any tagname is set.
 	 */
 	public is(tagName: string): boolean {
-		return (this.tagName && tagName === "*") || this.tagName === tagName;
+		if (!this.tagName) {
+			return false;
+		}
+		return (
+			tagName === "*" || this.tagName.toLowerCase() === tagName.toLowerCase()
+		);
 	}
 
 	/**