[Seaside] Finding the parent component of a rendered component

[Luke]

If I am using html render: <blah> to render a sub-component of the current
component, is there any way to reference the component who is the
sub-component's parent?

So, I have
ComponentA
  |
  |
  ---ComponentB

And from ComponentB#renderContentOn I want to be able to do something like
parent someFunction
and have that call the function someFunction on whatever component rendered the
current component.

I'm sure there's probably some way to do that, but I don't know what it is.