* Nested values
+
Custom types that don’t conform to the other two categories but have their own properties that are inputs or outputs. In effect, the task inputs or outputs are nested inside these custom types.

As an example, imagine you have a task that processes templates of varying types, such as FreeMarker, Velocity, Moustache, etc. It takes template source files and combines them with some model data to generate populated versions of the template files.

	// if the approval state hasn't changed, never fail on approval validation
	// this is allowed so that a v1 client that is simply updating spec and not mutating this value doesn't get rejected.  Imagine a controller controlling a CRD spec.
	if oldApprovalState != nil && *oldApprovalState == newApprovalState {
		return nil
	}

	// in v1, we require valid approval strings
	switch newApprovalState {

In other words, when you combine file collections this way, the result always reflects what's currently in the source file collections, even if they change during the build.

For example, imagine `collection` in the above example gains an extra file or two after `union` is created.
As long as you use `union` after those files are added to `collection`, `union` will also contain those additional files.

func (l *Loader) AddInteriorSym(container Sym, interior Sym) {
	// Container symbols are expected to have content/data.
	// NB: this restriction may turn out to be too strict (it's possible
	// to imagine a zero-sized container with an interior symbol pointing
	// into it); it's ok to relax or remove it if we counter an
	// oddball host object that triggers this.
	if l.SymSize(container) == 0 && len(l.Data(container)) == 0 {