You can harness the true power of Symbols by nesting them.
To create a nested Symbol, place a Symbol instance inside any other Symbol master on the Symbols page. Any updates you make to the Symbol master will be reflected throughout your design, no matter if they’re inside another Symbol or not. As well as placing an instance directly into a master, and inserting via the toolbar item, you can also create a nested Symbol by selecting multiple Symbols and pressing Create Symbol in the toolbar.
There’s no limit to how deep you can nest Symbols but please note, a Symbol cannot contain an instance of itself.
As mentioned in the Symbol Overrides section, nested Symbols can also be overridden, along with other properties.
Overriding a nested Symbol will allow you to swap out any Symbols, contained in an instance, with any other Symbol that is the same size as that Symbol’s master, or instance. For example, if you have a nested icon Symbol inside a toolbar, that’s also a Symbol, you can use overrides to swap out the icon with another icon, or no icon at all.
Clicking the icon that appears next to a nested Symbol’s name in the Inspector will take you directly to that Symbol’s master — a real timesaver compared to navigating to it manually.
You can determine which overrides will appear for your Symbol, directly in the Symbol Master. Go to the Symbol Artboard, and you’ll see the Manage Overrides section in the Inspector. Overridable properties are organized by layer and will affect what can be edited in any instances of that Symbol.