define-slot: Define a macro customization point

  Syntax

    'metal:define-slot' syntax::
   
      argument ::= Name

  Description

    The 'metal:define-slot' statement defines a macro customization
    point or *slot*. When a macro is used, its slots can be replaced,
    in order to customize the macro. Slot definitions provide default
    content for the slot. You will get the default slot contents if
    you decide not to customize the macro when using it.

    The 'metal:define-slot' statement must be used inside a
    'metal:define-macro' statement.

    Slot names must be unique within a macro.

  Examples

    Simple macro with slot::

      <p metal:define-macro="hello">
        Hello <b metal:define-slot="name">World</b>
      </p>
 
    This example defines a macro with one slot named 'name'. When you
    use this macro you can customize the 'b' element by filling the
    'name' slot.

  See Also

    "metal:fill-slot":metal-fill-slot.stx