Index: generic/predefined.xotcl
===================================================================
diff -u -r147831f1098cb9b96a28d4d5b0f9f3ccea35b9da -r901ceb8f58714e31d28ed3277923fc69c085d252
--- generic/predefined.xotcl	(.../predefined.xotcl)	(revision 147831f1098cb9b96a28d4d5b0f9f3ccea35b9da)
+++ generic/predefined.xotcl	(.../predefined.xotcl)	(revision 901ceb8f58714e31d28ed3277923fc69c085d252)
@@ -309,16 +309,11 @@
   ::xotcl::MetaSlot create ::xotcl::ObjectParameterSlot
   ::xotcl::relation ::xotcl::ObjectParameterSlot superclass ::xotcl::Slot
 
-
   #
   # create class and object for method parameter slots
   ::xotcl::MetaSlot create ::xotcl::MethodParameterSlot
   ::xotcl::relation ::xotcl::MethodParameterSlot superclass ::xotcl::Slot
 
-  foreach cmd [info command ::xotcl::cmd::MethodParameterSlot::*] {
-    ::xotcl::alias ::xotcl::MethodParameterSlot [namespace tail $cmd] $cmd
-  }
-  
   # create an object for dispatching
   ::xotcl::MethodParameterSlot create ::xotcl::methodParameterSlot
   
@@ -842,15 +837,54 @@
 
   ##################################################################
   # now the slots are defined; now we can defines the Objects or 
-  # classes with parameters more easily.
+  # classes with parameters more easily than above.
   ##################################################################
+
+  # remove helper proc
   proc createBootstrapAttributeSlots {} {}
+
+  ##################################################################
+  # create user-level converter/checker based on ::xotcl::ls
+  ##################################################################
+  # ::xotcl::is supports predicates for objects
+  #
+  #   ::xotcl::is <obj> object
+  #   ::xotcl::is <obj> type <class> 
+  #   ::xotcl::is <obj> class
+  #   ::xotcl::is <obj> baseclass
+  #   ::xotcl::is <obj> metaclass
+  #   ::xotcl::is <obj> mixin <class>
+  #
+  # Map these to type checkers. "object" and "class"
+  # are already predefined, define the rest.
+ 
+  ::xotcl::Slot method type=mixin {name value arg} {
+    if {![::xotcl::is $value mixin $arg]} {
+      error "Value '$value' of $name has not mixin $arg"
+    }
+    return $value
+  }
+  ::xotcl::Slot method type=baseclass {name value} {
+    if {![::xotcl::is $value baseclass]} {
+      error "Value '$value' of $name is not a baseclass"
+    }
+    return $value
+  }
+  ::xotcl::Slot method type=metaclass {name value} {
+    if {![::xotcl::is $value metaclass]} {
+      error "Value '$value' of $name is not a metaclass"
+    }
+    return $value
+  }
+
 }
 
+##################################################################
 # Create a mixin class to overload method "new" such it does not
 # allocate new objects in ::xotcl::*, but in the specified object
 # (without syntactic overhead).
-#
+##################################################################
+
 ::xotcl2::Class create ::xotcl::ScopedNew -superclass ::xotcl2::Class -parameter {
   {withclass ::xotcl2::Object}
   container
@@ -864,12 +898,14 @@
     eval ::xotcl::next -childof $object $args
   }
 }
-#
+
+##################################################################
 # The method 'contains' changes the namespace in which objects with
 # realtive names are created.  Therefore, 'contains' provides a
 # friendly notation for creating nested object structures. Optionally,
 # creating new objects in the specified scope can be turned off.
-#
+##################################################################
+
 ::xotcl2::Object public method contains {
    {-withnew:boolean true}
    -object
@@ -895,9 +931,10 @@
 ::xotcl2::Class forward slots %self contains \
     -object {%::xotcl::dispatch [::xotcl::self] -objscope ::subst [::xotcl::self]::slot}
 
-#
+##################################################################
 # copy/move implementation
-#
+##################################################################
+
 ::xotcl2::Class create ::xotcl::CopyHandler -parameter {
   {targetList ""}
   {dest ""}