Index: doc/Announce2.3.0
===================================================================
diff -u -r63fa317128555211b749beedd51f32e82af6b340 -rfc11b2380eef48346410636908936e9468c74807
--- doc/Announce2.3.0	(.../Announce2.3.0)	(revision 63fa317128555211b749beedd51f32e82af6b340)
+++ doc/Announce2.3.0	(.../Announce2.3.0)	(revision fc11b2380eef48346410636908936e9468c74807)
@@ -50,6 +50,30 @@
 
 - NX:
 
+  * Properties and variables now provide "exists" as an additional
+    accessor method, in addition to "get":
+
+    % package req nx
+    2.3
+    % nx::Class create C {
+       :property -accessor public {a 1} 
+    }
+    ::C
+    % ::C create ::c1
+    ::c1
+    % if {[::c1 a exists]} { ::c1 a get } else { ::c1 a set "1" }
+                  ^^^^^^
+
+    This is mainly to provide for symmetry in the property and
+    variable API, which otherwise requires one to resort to low-level
+    tests for existence, e.g.:
+
+    if {[::c1 eval {info exists :a}]} ...
+
+    This breaks the property/ variable abstraction, because one cannot
+    move to a different value store other than object variables w/o
+    rewriting client code.
+
   * Method combination for ensemble methods: Using [next] at the end
     of chains of ensemble methods fired the unknown handler,
     unintentionally. This was fixed.
Index: doc/Class.3
===================================================================
diff -u -rbaee0c34119f4b237787204b8c3e64bc04c05782 -rfc11b2380eef48346410636908936e9468c74807
--- doc/Class.3	(.../Class.3)	(revision baee0c34119f4b237787204b8c3e64bc04c05782)
+++ doc/Class.3	(.../Class.3)	(revision fc11b2380eef48346410636908936e9468c74807)
@@ -2,7 +2,7 @@
 '\" Generated from file 'Class\&.man' by tcllib/doctools with format 'nroff'
 '\" Copyright (c) 2014-2016 Stefan Sobernig <stefan\&.sobernig@wu\&.ac\&.at>, Gustaf Neumann <gustaf\&.neumann@wu\&.ac\&.at>; available under the Creative Commons Attribution 3\&.0 Austria license (CC BY 3\&.0 AT)\&.
 '\"
-.TH "nx::Class" 3 2\&.3a0 Class "NX API"
+.TH "nx::Class" 3 2\&.3 Class "NX API"
 .\" The -*- nroff -*- definitions below are for supplemental macros used
 .\" in Tcl/Tk manual entries.
 .\"
@@ -955,10 +955,14 @@
 which become assigned to the property\&. The second, optional element
 sets a \fIdefaultValue\fR for this property\&.
 .sp
-If \fB-accessor\fR is set, a property will provide for
-a pair of getter and setter methods:
+If \fB-accessor\fR is set, a property will provide for different
+getter and setter methods:
 .RS
 .TP
+\fIobj\fR \fIpropertyName\fR \fBexists\fR
+Returns 1 if the value store of \fIpropertyName\fR (e\&.g\&., an object
+variable) exists and has been given a value, returns 0 otherwise\&.
+.TP
 \fIobj\fR \fIpropertyName\fR \fBset\fR \fIvalue\fR
 Sets the property \fIpropertyName\fR to \fIvalue\fR\&.
 .TP
@@ -1063,10 +1067,14 @@
 managed by the variable\&. Optionally, a \fIdefaultValue\fR can
 be defined\&.
 .sp
-If \fB-accessor\fR is set explicitly, a variable will provide for a pair of
-getter and setter methods:
+If \fB-accessor\fR is set explicitly, a variable will
+provide for getter and setter methods:
 .RS
 .TP
+\fIobj\fR \fIvariableName\fR \fBexists\fR
+Returns 1 if the value store of \fIvariableName\fR (e\&.g\&., an object
+variable) exists and has been given a value, returns 0 otherwise\&.
+.TP
 \fIobj\fR \fIvariableName\fR \fBset\fR \fIvarValue\fR
 Sets \fIvariableName\fR to \fIvarValue\fR\&.
 .TP
Index: doc/Object.3
===================================================================
diff -u -r6cbeef2d45ae090cf57de7703e0b480125e277b1 -rfc11b2380eef48346410636908936e9468c74807
--- doc/Object.3	(.../Object.3)	(revision 6cbeef2d45ae090cf57de7703e0b480125e277b1)
+++ doc/Object.3	(.../Object.3)	(revision fc11b2380eef48346410636908936e9468c74807)
@@ -1268,10 +1268,14 @@
 which become assigned to the property\&. The second, optional element
 sets a \fIdefaultValue\fR for this property\&.
 .sp
-If \fB-accessor\fR is set, a property will provide for
-a pair of getter and setter methods:
+If \fB-accessor\fR is set, a property will provide for different
+getter and setter methods:
 .RS
 .TP
+\fIobj\fR \fIpropertyName\fR \fBexists\fR
+Returns 1 if the value store of \fIpropertyName\fR (e\&.g\&., an object
+variable) exists and has been given a value, returns 0 otherwise\&.
+.TP
 \fIobj\fR \fIpropertyName\fR \fBset\fR \fIvalue\fR
 Sets the property \fIpropertyName\fR to \fIvalue\fR\&.
 .TP
@@ -1510,10 +1514,14 @@
 managed by the variable\&. Optionally, a \fIdefaultValue\fR can
 be defined\&.
 .sp
-If \fB-accessor\fR is set explicitly, a variable will provide for a pair of
-getter and setter methods:
+If \fB-accessor\fR is set explicitly, a variable will
+provide for getter and setter methods:
 .RS
 .TP
+\fIobj\fR \fIvariableName\fR \fBexists\fR
+Returns 1 if the value store of \fIvariableName\fR (e\&.g\&., an object
+variable) exists and has been given a value, returns 0 otherwise\&.
+.TP
 \fIobj\fR \fIvariableName\fR \fBset\fR \fIvarValue\fR
 Sets \fIvariableName\fR to \fIvarValue\fR\&.
 .TP
Index: doc/property.man.inc
===================================================================
diff -u -r8f64a468d8bb53f2ba317c8c738c2d3a24243980 -rfc11b2380eef48346410636908936e9468c74807
--- doc/property.man.inc	(.../property.man.inc)	(revision 8f64a468d8bb53f2ba317c8c738c2d3a24243980)
+++ doc/property.man.inc	(.../property.man.inc)	(revision fc11b2380eef48346410636908936e9468c74807)
@@ -27,9 +27,12 @@
 
 [para] 
 
-If [option "-accessor"] is set, a property will provide for
-a pair of getter and setter methods:
+If [option "-accessor"] is set, a property will provide for different
+getter and setter methods:
 [list_begin definitions]
+[def "[arg obj] [arg propertyName] [method exists]"]
+Returns 1 if the value store of [arg propertyName] (e.g., an object
+variable) exists and has been given a value, returns 0 otherwise.
 [def "[arg obj] [arg propertyName] [method set] [arg value]"]
 Sets the [term property] [arg propertyName] to [arg value].
 [def "[arg obj] [arg propertyName] [method get]"]
Index: doc/variable.man.inc
===================================================================
diff -u -r8f64a468d8bb53f2ba317c8c738c2d3a24243980 -rfc11b2380eef48346410636908936e9468c74807
--- doc/variable.man.inc	(.../variable.man.inc)	(revision 8f64a468d8bb53f2ba317c8c738c2d3a24243980)
+++ doc/variable.man.inc	(.../variable.man.inc)	(revision fc11b2380eef48346410636908936e9468c74807)
@@ -18,10 +18,13 @@
 
 [para] 
 
-If [option "-accessor"] is set explicitly, a [term variable] will provide for a pair of
-getter and setter methods:
+If [option "-accessor"] is set explicitly, a [term variable] will
+provide for getter and setter methods:
 
 [list_begin definitions]
+[def "[arg obj] [arg variableName] [method exists]"]
+Returns 1 if the value store of [arg variableName] (e.g., an object
+variable) exists and has been given a value, returns 0 otherwise.
 [def "[arg obj] [arg variableName] [method set] [arg varValue]"]
 Sets [arg variableName] to [arg varValue].
 [def "[arg obj] [arg variableName] [method get]"]
Index: library/nx/nx.tcl
===================================================================
diff -u -r77a193c118f4ae2b0ccd0913e39326e4f0f53fe6 -rfc11b2380eef48346410636908936e9468c74807
--- library/nx/nx.tcl	(.../nx.tcl)	(revision 77a193c118f4ae2b0ccd0913e39326e4f0f53fe6)
+++ library/nx/nx.tcl	(.../nx.tcl)	(revision fc11b2380eef48346410636908936e9468c74807)
@@ -2273,6 +2273,10 @@
     ::nsf::var::unset -nocomplain=$nocomplain $obj $prop
   }
 
+  ::nx::VariableSlot public method value=exists {obj prop} {
+    ::nsf::var::exists $obj $prop
+  }
+
   ::nx::VariableSlot public method value=add {obj prop value {pos 0}} {
     if {![:isMultivalued]} {
       #puts stderr "... vars [[self] info vars] // [[self] eval {set :multiplicity}]"
Index: tests/methods.test
===================================================================
diff -u -r8e2e356e9bcef39f43dfe3690b82d9586c7adc72 -rfc11b2380eef48346410636908936e9468c74807
--- tests/methods.test	(.../methods.test)	(revision 8e2e356e9bcef39f43dfe3690b82d9586c7adc72)
+++ tests/methods.test	(.../methods.test)	(revision fc11b2380eef48346410636908936e9468c74807)
@@ -646,7 +646,7 @@
   }
 
   # dispatch methods without current object 
-  ? ::o::a {wrong # args: use "::o ::o::a add|delete|get|set|unset"}
+  ? ::o::a {wrong # args: use "::o ::o::a add|delete|exists|get|set|unset"}
   ? ::o::b "::o2"
   ? ::o::foo "no current object; command called outside the context of a Next Scripting method"
   ? ::o::x "no current object; x called outside the context of a Next Scripting method"
Index: tests/properties.test
===================================================================
diff -u -r8e2e356e9bcef39f43dfe3690b82d9586c7adc72 -rfc11b2380eef48346410636908936e9468c74807
--- tests/properties.test	(.../properties.test)	(revision 8e2e356e9bcef39f43dfe3690b82d9586c7adc72)
+++ tests/properties.test	(.../properties.test)	(revision fc11b2380eef48346410636908936e9468c74807)
@@ -11,7 +11,6 @@
 #puts stderr "*** default defaultAccessor '[nx::configure defaultAccessor]'"
 nx::configure defaultAccessor none
 
-
 #####################################################################
 # class-level properties
 #####################################################################
@@ -788,7 +787,86 @@
   ? {C cget -b} b2
 }
 
+nx::test case exists-on-props {
+  nx::Class create C {
+    :object property {A A1}
+    :property {a a1}
+    
+    :object property -accessor public {B B1}
+    :property -accessor public {b b1}
+    :object property -accessor public BB
+    :property -accessor public bb
 
+    :object property -accessor protected {C C1}
+    :property -accessor protected {c c1}
+    
+    :object property -accessor private {D D1}
+    :property -accessor private {d d1}
+
+    :create c1
+
+    :public object method do {args} {
+      : {*}$args
+    }
+
+    :public method do {args} {
+      : {*}$args
+    }
+
+    :public object method doLocal {args} {
+      : -local {*}$args
+    }
+    
+    :public method doLocal {args} {
+      : -local {*}$args
+    }
+    
+  }
+
+  ? {::C A exists} \
+      "method 'A' unknown for ::C; in order to create an instance of class ::C, consider using '::C create A ?...?'"
+  ? {::c1 a exists} "::c1: unable to dispatch method 'a'"
+
+  ? {::C B exists} 1
+  ? {::c1 b exists} 1
+
+  ? {::C B get} "B1"
+  ? {::c1 b get} "b1"
+
+  ? {::C BB exists} 0
+  ? {::c1 bb exists} 0
+  
+  ? {::C do C exists} 1
+  ? {::C eval {info exists :C}} 1
+  ? {::c1 do c exists} 1
+  ? {::c1 eval {info exists :c}} 1
+
+  ? {::C do C unset} ""
+  ? {::c1 do c unset} ""
+
+  ? {::C do C exists} 0
+  ? {::C eval {info exists :C}} 0
+  ? {::c1 do c exists} 0
+  ? {::c1 eval {info exists :c}} 0
+
+  # interaction: exists + private
+  
+  ? {::C doLocal D exists} 1
+  ? {::c1 doLocal d exists} 1
+
+  ? {::C doLocal D unset} ""
+  ? {::c1 doLocal d unset} ""
+
+  ? {::C doLocal D exists} 0
+  ? {::c1 doLocal d exists} 0
+
+  ? {::C D exists} \
+      "method 'D' unknown for ::C; in order to create an instance of class ::C, consider using '::C create D ?...?'"
+  ? {::c1 d exists} "::c1: unable to dispatch method 'd'"
+  
+}
+
+
 #####################################################################
 # performance tests
 #####################################################################