class Sass::Engine

def validate_and_append_child(parent, child, line, root)
  unless root
    case child
    when Tree::MixinDefNode
      raise SyntaxError.new("Mixins may only be defined at the root of a document.", line.index)
    when Tree::ImportNode
      raise SyntaxError.new("Import directives may only be used at the root of a document.", line.index)
    end
  end
  case child
  when Array
    child.each {|c| validate_and_append_child(parent, c, line, root)}
  when Tree::Node
    parent << child
  end
end