https://news.ycombinator.com/submit

> Leave url blank to submit a question for discussion. If there is no url, text will appear at the top of the thread. If there is a url, text is optional.

Ah.

For years I have been submitting links through a bookmarklet that goes to /submitlink rather than submit, so I don't get the text box.

I wonder why this feature isn't used more often.