I tried to link to the Wikipedia article on Möbius transformations, at
https://en.wikipedia.org/wiki/Möbius_transformation, using the markdown
But Markdown didn't render the link properly. It looks like this: Möbius transformations
I had to write the URL as
https://en.wikipedia.org/wiki/M%3Fbius_transformation to get Markdown to generate a hyperlink.
I realize that Markdown needs to have some criterion for deciding where the URL ends, and that it needs to be fairly lax about this to avoid accidentally including the entire following text in the URL, but I think it should at least understand that Unicode characters that have the “letter” property can be part of URLs. The
href attribute in the rendered hyperlink could still be URL-encoded, for compatibility reasons.