Structured selector containing all required information for pattern-matching onto
string-named properties owned by nodes in a data hierarchy, where data hierarchies belong
to specific components.
RuntimeError indicates errors that manifest after the Sample server has
begun periodically sampling data. Clients can ignore these errors, though
they could potentially indicate that no SampleReady request will ever arrive,
or that the batch iterator might behave in unexpected ways, such as hanging.
TreeNames are the set of names of fuchsia.inspect.Trees for a component that
were parsed out of a selector. The hierarchy and property selector portions
will only be applied to trees that match this set.