Reserved Symbols in GDL/GWL
               ===========================

When defining your own objects in GDL, there are a few message names
you should avoid using (i.e. overriding). This only applies to message
and input names within a define-object form, since the :GDL and :GWL
packages have definition locks set. The package definition locks avoid
accidental redefinition of symbols naming GDL/GWL functions, macros,
parameters, constants, and classes. 

In a future GDL release, automatic protection against redefining these
pre-defined messages will probably be added. But currently it is up to
the application developer to avoid using these names.


1. Symbols to Avoid Using as Messages Within a Define-Object Form
   ==============================================================

This includes :input-slots, :computed-slots, :objects,
:hidden-objects, and :functions.

  o From Vanilla-Mixin (which means these apply to any define-object
    form). Please see the GDL Reference Section on Vanilla-Mixin for
    more details:

     aggregate 
     children 
     documentation 
     first 
     first? 
     follow-root-path 
     hidden-children 
     index 
     last 
     last? 
     leaf? 
     message-list 
     mixins 
     next 
     parent
     parent-tree 
     previous 
     restore-slot-default! 
     root 
     root-path 
     root? 
     set-slot! 
     set-slots! 
     slot-documentation 
     type 
     update!


  o From Base-Object (which means these apply to any define-object
    which mixes in base-object or any of its subclasses). Please see
    the GDL Reference Section on Base-Object for more details (note
    that color and line-thickness can be specified in the
    display-controls, and should not be specified as their own
    messages):

    axis-vector    
    color-decimal
    edge-center
    face-center
    face-normal-vector
    line-thickness 
    local-center
    obliqueness
    vertex
    
    
       
2. Symbols to Avoid Using as Input Specifications to an Object or Hidden-Object
===============================================================================

 The following have special meaning within an :objects or
 :hidden-objects specification and should not be used except for the
 intended purpose:

    :parameters

        Used to pass a plist of input specifications into a child
        object, e.g:

          :parameters (list :length 10 :width 20 :height 30)

        is functionally equivalent to:

          :length 10
          :width 20
          :height 30

    :pass-down
  
        Used as shorthand for passing messages down to the child part,
        e.g:

          :pass-down (data labels colors)

        is equivalent to:

          :data (the data)
          :labels (the labels)
          :colors (the colors)


    :sequence

        Used for making a sequence of parts, as with
           
           ...
           :sequence (:size (length (the data)))
           ...
            
          for a standard sequence, or

           ...
           :sequence (:indices (list 1 2 3))
           ...

          for a variable sequence.


    :type 

        Used to specify the type or types of the child object(s).



3. Internal naming convention with the percent sign ("%")
=========================================================

 Finally, in addition to the above specific messages, you should avoid
 naming any messages starting and ending with a percent character
 ("%"), e.g. %my-message% -- this is a convention used to name
 internal, private GDL messages.