An Editing Scope is the container you are currently editing inside. For example, if you have made a Group of objects, you can edit inside the group (to edit the individual objects) by entering that group’s Editing Scope. Likewise, if you have drawn a Path, you can enter the path’s Editing Scope in order to move and edit the path’s points, or if you have a Text object, you can enter its Editing Scope in order to edit the text.
When you are inside an Editing Scope, a gold rectangular border is drawn around the relevant canvas objects. The Editing Scope is shown in the Scope Bar at the top of the canvas.

Additionally, the scope you are in (plus its parents, all the way up to the layer) are tinted in the Layers palette:

The following things on the canvas have their own editing scopes which you can enter:
We’ll cover what you can do inside each object’s editing scope below.
In McKinley you can group objects, just like in many other vector graphics programs. Grouped objects can be moved around, hidden, and transformed as one single unit.
To make a new group, select two or more objects on the canvas and choose Arrange -> Group (⌘G).
To get rid of a group, you can select it and choose Arrange -> Ungroup (⇧⌘G). Groups will also disappear once they have no items inside them.
To modify the items inside a group, you need to enter the group’s Editing Scope by means of one of the methods above (e.g. double clicking on it). Once you’re inside the group’s Editing Scope, you can work with the individual objects inside it (select them, use their handles to transform them, etc). You can also create new objects directly within the group’s editing scope.
You can nest groups within each other. Just group some objects while you’re inside another group’s Editing Scope! You can enter nested Editing Scopes as normal, by double clicking on them or via one of the other methods.
Groups are useful for your own organisation, but there are some SF Symbol specific things that they can do:
The most useful is Override Children’s Colour Mode. Find this in the Colour inspector pane when your group is selected:

This feature enables certain things that you can do on SF Symbol layers in the Apple app, namely:
If you turn Override Children’s Colour Mode on on a group, you will see colour controls appear in the inspector pane, applying to the group itself:

These colours (including the Knockout setting) will be applied to every item within the group. If you select an item inside a group that has Override Children’s Colour Mode turned on, that item will no longer have its own individual colour settings, only checkboxes for whether it has a fill and/or a stroke:

The same is true of the per-object animation steps: if the object is within a group with Override Children’s Colour Mode, that also means the group now owns the object’s Pulse, Rotate, and Variable Rendering step settings (so they can’t be set individually on the child object any more).
You might be (justifiably!) confused why this is a setting on Group.
This is because of where the ‘unit of colour’ goes in McKinley vs the SF Symbols app. In SF Symbols, you can only apply colour to a whole layer at once. Therefore there’s no need to have a separate setting to control something like this. In SF Symbols, if you didn’t want paths to be the same colour or to animate together, you’d just make them be separate layers.
In McKinley, you don’t have to manage things yourself like that. For the most part, you can just apply colours and animation settings directly to objects, which is much more natural (and similar to how other vector graphics apps behave).
However, because of that flexibility, you have to tell McKinley when you do want to colour or animate things as if they’re one unit. That’s what this setting is for.
In keeping with McKinley’s philosophy of most flexibility, it’s a setting on Group rather than Layer. You shouldn’t need to make new McKinley Layers just because you want to change some colours together.
There is a setting on Layer called Composites As One Unit. At first sight it might seem like they do similar things.
The Composites As One Unit setting makes the whole layer use a different rendering mode, called Shape Group (or LayerTree), within the outputted SF Symbol.
When using the Apple SF Symbols app, you cannot turn this setting on manually. It is used when you use the SF Symbols app to make an Enclosure. In McKinley we give you manual control over it if you want.
Both a group’s Override Children’s Colour Mode setting and a layer’s Composites As One Unit setting let you override the colour of their children. However they’re doing different things on export, and thus they have different capabilities:
One further thing to note: editing Shape Group layers within the SF Symbols app is not supported (apart from the Apple-provided enclosures). It’s fine to use them in your symbols, and they’ll work fine within your app, but if you try to edit them in SF Symbols you might get an error.
You can read more about Clipping Groups on their own page.
A Clipping Mask is a vector shape that defines a ‘window’ that other shapes can be seen through.
A Clipping Group is the thing that contains both the clipping mask, and the contents that the mask is partially obscuring.
A clipping group has two Editing Scopes inside it, Mask and Contents.
Double click on a Clipping Group to edit its Contents.
You switch between editing the contents and the mask with the segmented control at the bottom of the canvas or Arrange -> Edit Mask Shape / Edit Clip Content.
You can read more about Text objects on their own page.
[TBC]