@SysInclude { fontdefs }
@SysInclude { langdefs }
@SysInclude { dl }
@SysInclude { docf }

export @Foo @Bar
def @Base
@Begin

  # This symbol is our guinea pig.
  def @Foo { This is a basic FOO. }

  # Demonstrates the lexical scoping.
  def @Bar { "@Foo" is address@hidden''. }

  # YOU CAN'T!  It's an error: symbol ... previously defined at ...
  # def @Foo { No way! }

@End @Base

extend @Base
export @Foo @BaseFoo @Before @After
def @Derived
@Begin

  # We still see the @Foo from @Base here.
  def @Before { "@Foo" was address@hidden''. }

  # Make old @Foo still available through renaming.
  # Also, you can use @Open for explicit qualification (see below).
  def @BaseFoo { @Foo }

  # YOU CAN!  Redefining.
  def @Foo { This is a redefined FOO. }

  # Here @Foo is the redefined one.
  def @After { "@Foo" is now address@hidden''. }

@End @Derived

@Use { @DocumentLayout @OddLeftMargin { 2.5c @OrIfPlain 0f } }
@Use { @OrdinaryLayout }

@Use { @Base }
@Use { @Derived }

@Document // @Text @Begin
@LP Explicit qualification: @Base @Open { @Foo }
@LP Basic one renamed in "@Derived": @BaseFoo
@LP Before redefinition: @Before
@LP Redefined: @Foo
@LP After redefinition: @After
@LP Despite redefinition: @Bar
@End @Text