In the HTML: `<h1>Hello</h1>`.
In the CSS: `h1 { text-transform: uppercase; }`.
Select the H1 and copy. On the 📋 clipboard:
Chrome: HELLO
Safari: HELLO
Firefox: Hello
@aardrian is on this since 2012 (https://adrianroselli.com/2012/06/copying-content-styled-with-text.html). I just filed a Chrome bug (https://crbug.com/1429183) after the WebKit bug by @mathias from 2010 (https://bugs.webkit.org/show_bug.cgi?id=43202).
@tomayac @aardrian @mathias Hmm, I think Firefox behavior may be partially a bug. Firefox will copy this as all uppercase to rich text contexts but sentence case plaintext: `<h1 style="text-transform: uppercase">Hello<h1>`. But the original example it copies as mixed-case always. So it's following the spec rule for plaintext, but additionally has a bug where it won't copy styles that come from style rules, even when pasting into an editable HTML context like a macOS Mail compose window. Firefox likewise copies `color: red` when it comes from inline style but not when it comes from an external style rule.