Index: library/nx/nx.tcl
===================================================================
diff -u -rb6d81c6521d1e1d58f00763f5ab30a0946cc222a -r67ef5da1e732c50c33f9a3e5769b68ddf18cdaa7
--- library/nx/nx.tcl	(.../nx.tcl)	(revision b6d81c6521d1e1d58f00763f5ab30a0946cc222a)
+++ library/nx/nx.tcl	(.../nx.tcl)	(revision 67ef5da1e732c50c33f9a3e5769b68ddf18cdaa7)
@@ -1002,10 +1002,8 @@
       set properties [string range $value [expr {$colonPos+1}] end]
       set name [string range $value 0 [expr {$colonPos -1}]]
       foreach property [split $properties ,] {
-        if {$property eq "required"} {
-          lappend opts -required 1
-        } elseif {$property eq "multivalued"} {
-          lappend opts -multivalued 1
+        if {$property in [list "required" "multivalued" "allowempty" "convert"]} {
+          lappend opts -$property 1
         } elseif {[string match type=* $property]} {
           set type [string range $property 5 end]
           if {![string match ::* $type]} {set type ::$type}