Created attachment 261734 [details] Testcase On El Capitan with Safari 9 or nightly build r190010, when setting a span as Hoefler Text with a 400 weight, it gets rendered with a bold weight, when setting it as Hoefler Text with a weight of 700, it gets rendered as non-bold. Everything is as expected on Yosemite with Safari 8. Attaching test file and screen cap from rendering on El Capitan.
Created attachment 261735 [details] Rendering on El Capitan
Looks like fallout from CTFontCreateForCSS().
<rdar://problem/22830262>
The fix for this issue was needed outside the WebKit project, therefore this is being resolved as 'Moved'. This should now be fixed in shipping software.