About two months ago, this happened:

And a few hours later:

It took a few more hours and days after this to refine some details, but I have now tagged the first release of this extension. Give it a try and let me know what you think. Bug reports and feature requests are welcome.

(I chose to name the data type uri instead of url, as originally suggested, because that is more correct and matches what the parsing library calls it. One could create a domain if one prefers the other name or if one wants to restrict the values to certain kinds of URIs or URLs.)

(If you are interested in storing email addresses, here is an idea.)