Index: generic/predefined.h
===================================================================
diff -u -r210eab6d9149846d5d6a6a8e0fa74e232ca5b6de -rf6be532e62dfbe148ebca8205a67688b751298ad
--- generic/predefined.h	(.../predefined.h)	(revision 210eab6d9149846d5d6a6a8e0fa74e232ca5b6de)
+++ generic/predefined.h	(.../predefined.h)	(revision f6be532e62dfbe148ebca8205a67688b751298ad)
@@ -163,6 +163,8 @@
 "lappend opts required}\n"
 "if {[$slot exists type]} {\n"
 "lappend opts [$slot type]}\n"
+"if {[$slot exists arg]} {\n"
+"lappend opts arg=[$slot arg]}\n"
 "if {[$slot exists default]} {\n"
 "set arg [::xotcl::setinstvar $slot default]\n"
 "if {[string match {*\\[*\\]*} $arg]} {\n"
@@ -327,7 +329,8 @@
 "{value_check once}\n"
 "initcmd\n"
 "valuecmd\n"
-"valuechangedcmd}\n"
+"valuechangedcmd\n"
+"arg}\n"
 "::xotcl::Attribute method __default_from_cmd {obj cmd var sub op} {\n"
 "$obj trace remove variable $var $op [list [::xotcl::self] [::xotcl::self proc] $obj $cmd]\n"
 "::xotcl::setinstvar $obj $var [$obj eval $cmd]}\n"
@@ -421,15 +424,22 @@
 "foreach arg $arglist {\n"
 "set l [llength $arg]\n"
 "set name [lindex $arg 0]\n"
-"if {[string first : $name] > -1} {\n"
-"foreach {name type} [split $name :] break\n"
-"if {$type eq \"required\"} {\n"
-"set required 1\n"
-"unset type}}\n"
+"set colonPos [string first : $name]\n"
+"if {$colonPos > -1} {\n"
+"set properties [string range $name [expr {$colonPos+1}] end]\n"
+"set name [string range $name 0 [expr {$colonPos -1}]]\n"
+"foreach property [split $properties ,] {\n"
+"if {$property eq \"required\"} {\n"
+"set required 1} elseif {[string match arg=* $property]} {\n"
+"set argument [string range $property 4 end]} else {\n"
+"set type $property}}}\n"
 "set cmd [list ::xotcl::Attribute create [::xotcl::self]::slot::$name]\n"
 "if {[info exists type]} {\n"
 "lappend cmd -type $type\n"
 "unset type}\n"
+"if {[info exists argument]} {\n"
+"lappend cmd -arg $argument\n"
+"unset argument}\n"
 "if {[info exists required]} {\n"
 "lappend cmd -required 1\n"
 "unset required}\n"