`Scratch` -- a "scratchpad" for your node- or page-scoped variables. In most cases you can do well without `Scratch`, but there are some use cases that aren't solvable with Go's templates without `Scratch`'s help, due to scoping issues.
`Set` and `SetInMap` can store values of any type.
For single values, `Add` accepts values that support Go's `+` operator. If the first `Add` for a key is an array or slice, the follwing adds will be appended to that list.
The scope of the backing data is global for the given `Node`, `Page` or `Shortcode`, and spans partial and shortcode includes.
Note that `.Scratch` from a shortcode will return the shortcode's `Scratch`, which in most casses is what you want. If you want to store it in the page scroped Scratch, then use `.Page.Scratch`.
**Note:** The examples above uses the special `$` variable, which refers to the top-level node. This is the behavior you most likely want, and will help remove some confusion when using `Scratch` inside page range loops -- and you start inadvertently calling the wrong `Scratch`. But there may be use cases for `{{ .Scratch.Add "key" "some value" }}`.
