Mark comment prop as unstable

.changeset/shy-hotels-impress.md

@@ -2,6 +2,4 @@
 'preact-render-to-string': minor
 ---
 
-Add ability to render comments via `<Fragment comment="my-comment" />`. When the `comment` prop is present all children of that `Fragment` will be ignored. This PR only supports that in server environments as it's useful to mark islands and other things. It's not supported in the browser.
-
-We picked a `Fragment` for this as it's the least common component and therefore the branch in our code with the least impact on perf by adding another if-check.
+Add experimental ability to render HTML comments via `<Fragment UNSTABLE_comment="my-comment" />`. When the `UNSTABLE_comment` prop is present all children of that `Fragment` will be ignored and a HTML comment will be rendered instead. This feature is added to allow framework authors to experiment with marking DOM for hydration in the client. Note that it's marked as unstable and might change in the future.

src/index.js

@@ -167,8 +167,8 @@ function _renderToString(vnode, context, isSvgMode, selectValue, parent) {
 		if (type === Fragment) {
 			// Fragments are the least used components of core that's why
 			// branching here for comments has the least effect on perf.
-			if (props.comment) {
-				return '<!--' + encodeEntities(props.comment || '') + '-->';
+			if (props.UNSTABLE_comment) {
+				return '<!--' + encodeEntities(props.UNSTABLE_comment || '') + '-->';
 			}
 
 			rendered = props.children;

test/render.test.js

@@ -1311,13 +1311,15 @@ describe('render', () => {
 
 	describe('HTML Comments', () => {
 		it('should render HTML comments via Fragments', () => {
-			expect(render(<Fragment comment="foo" />)).to.equal('<!--foo-->');
+			expect(render(<Fragment UNSTABLE_comment="foo" />)).to.equal(
+				'<!--foo-->'
+			);
 		});
 
 		it('should ignore children with comment prop', () => {
 			expect(
 				render(
-					<Fragment comment="foo">
+					<Fragment UNSTABLE_comment="foo">
 						<p>foo</p>
 					</Fragment>
 				)