Suppose the following DOM tree:

<div id='host'> (shadowhost)
  - <div>
     - <p>

<Shadow Root of 'host>
  - <content id='content' select='div'>


And suppose we want to style a distributed node, <p>, using a /select/ reference combinator as follows:

[Rule A]:
#content/select/div > p {
  color: blue
}


I have a question:
 Who supposes to use 'Rule A'? A component author or a component user?

I mean where this 'rule A' should be defined? I supposed that the rule should be defined in the shadow Root since this selector is supposed to be used by component authors. But I am not sure and would like to make it clear.