Where did the Object Library go in Xcode 10?

Shortcuts:

• Shift + Command + L: Show Library.

• Shift + Command + M: Show Media Library.

Xcode 10 has added a toolbar button to access the Object Library.

From a thread on Apple Developer Forum:

Library content has moved from the bottom of the Inspector area to an overlay window, which can be moved and resized like Spotlight search. It dismisses once items are dragged, but holding the Option key before dragging will keep the library open for an additional drag.

The library can be opened via a new toolbar button, the View > Libraries menu, or the ⇧⌘L keyboard shortcut. Content dynamically matches the active editor, so the same UI provides access to code snippets, Interface Builder, SpriteKit, or SceneKit items. The media library is available via a long press on the toolbar button, the View > Libraries menu, or the ⇧⌘M keyboard shortcut. (37318979, 39885726)

What the existing answers (so far) neglect to mention is that if you hold Option as you summon the Library window — i.e., press Shift + Option + Command + L, or hold Option while clicking the Library button in the toolbar — the window stays open, permanently, until you explicitly close it with its Close button.

It is not incorporated (docked) into the current project window, but it can be used in any project. The point is that it becomes almost a normal window (to be precise, it becomes a normal floating window).

XCode 11 - Object library location

Click on the plus icon on the top right corner of Xcode topbar.