Magik.JsonView.render_relationships

You're seeing just the function render_relationships, go back to Magik.JsonView module for more information.
Link to this function

render_relationships(struct, relationships)

Render relationship field for struct. relationships is a list of {field, view} for mapping render. For each field, call function View.render() to render json for relation object.

Example relationships:

relationships = [comments: CommentView, author: UserView]

Result of render_relationships(post, relationships) equal to output of below code

%{
    comments: CommentView.render_many(comments, CommentView, "comment.json"),
    autho: UserView.render_one(author, UserView, "user.json")
}