The use of an animator proxy is causing the initialize method to be called during animation, and when registering user defaults in initialize, we may trigger key/value observers to be notified, which for this code can result in a crash in OS code with the message: “Trying to recursively lock an os_unfair_lock”.
An alternative to accessing the cell directly is using NSAccessibilityUnignoredDescendant to obtain the object, but while it seems to abstract away whether or not it is the control or its cell which participates in accessibility, we forego the type checker.
At least on macOS 10.14 the auxiliary titlebar view is placed so that the bottom line of the view overlaps with the divider that separates the titlebar from the window content.
While the tab view background color is using alpha, the divider was still visible, but it didn’t look that good when using the light appearance.
The problem with having the check in updateToLayout: is that the background view that extends to right window edge is not part of the layout, so while the width of this view may change when resizing the window, it would not result in a different layout.
Newer versions of clang now warn when using API's that are only available on OS version newer than the target OS unless they are guarded using `@available`.
This is temporary and should be remove when we move away from older versions of Xcode.
