Is it valid XHTML / good practice to have links of the following form? //www.example.com/foo/bar.html
If the current page is HTTP, then the link points to: http://www.example.com/foo/bar.html If the current page is secured under HTTPS, then the link points to: https://www.example.com/foo/bar.html
In other words, is
<a href="//www.example.com/">
valid in XHTML 1.1 Strict? And, is it supported by many/all browsers?