In a comment, I want to write the title of a question (to point out that it's a duplicate or related stuff) instead of "pasting" its URL. How can I do that?
I'm answering so that we can keep an easy copy here as a quick reference, but it's actually there in Qmechanic's comment.
Comments use a simplified version of markdown. To include links, use
[As a link in a comment how to mention the title of a question instead of its URL?](https://physics.meta.stackexchange.com/questions/10699/as-a-link-in-a-comment-how-to-mention-the-title-of-a-question-instead-of-its-url)
The text which is expected to appear finally should be in square brackets, and the URL immediately follows that in normal brackets. You can't end the stuff inside the square brackets with a space, and you need to include the full URL: 'https://' and all. Note that this works in normal answers and questions as well.