diff --git a/src/testdir/test86.ok b/src/testdir/test86.ok
index 6ad02e3..4f6d4b3 100644
--- a/src/testdir/test86.ok
+++ b/src/testdir/test86.ok
@@ -764,7 +764,7 @@
 d["a"] = {"abcF" : Mapping({"\0" : 1})}:TypeError:('expected string without null bytes',)
 <<< Finished
 >>> Testing *Iter* using d["a"] = {"abcF" : %s}
-d["a"] = {"abcF" : FailingIter()}:TypeError:('unable to convert FailingIter to vim structure',)
+d["a"] = {"abcF" : FailingIter()}:TypeError:('unable to convert FailingIter to a Vim structure',)
 d["a"] = {"abcF" : FailingIterNext()}:NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using d["a"] = {"abcF" : %s}
@@ -791,7 +791,7 @@
 d["a"] = Mapping({"abcG" : Mapping({"\0" : 1})}):TypeError:('expected string without null bytes',)
 <<< Finished
 >>> Testing *Iter* using d["a"] = Mapping({"abcG" : %s})
-d["a"] = Mapping({"abcG" : FailingIter()}):TypeError:('unable to convert FailingIter to vim structure',)
+d["a"] = Mapping({"abcG" : FailingIter()}):TypeError:('unable to convert FailingIter to a Vim structure',)
 d["a"] = Mapping({"abcG" : FailingIterNext()}):NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using d["a"] = Mapping({"abcG" : %s})
@@ -803,7 +803,7 @@
 d["a"] = Mapping({"abcG" : FailingNumber()}):TypeError:('long() argument must be a string or a number',)
 <<< Finished
 >>> Testing *Iter* using d["a"] = %s
-d["a"] = FailingIter():TypeError:('unable to convert FailingIter to vim structure',)
+d["a"] = FailingIter():TypeError:('unable to convert FailingIter to a Vim structure',)
 d["a"] = FailingIterNext():NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using d["a"] = %s
@@ -840,7 +840,7 @@
 d.update({"abcF" : Mapping({"\0" : 1})}):TypeError:('expected string without null bytes',)
 <<< Finished
 >>> Testing *Iter* using d.update({"abcF" : %s})
-d.update({"abcF" : FailingIter()}):TypeError:('unable to convert FailingIter to vim structure',)
+d.update({"abcF" : FailingIter()}):TypeError:('unable to convert FailingIter to a Vim structure',)
 d.update({"abcF" : FailingIterNext()}):NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using d.update({"abcF" : %s})
@@ -867,7 +867,7 @@
 d.update(Mapping({"abcG" : Mapping({"\0" : 1})})):TypeError:('expected string without null bytes',)
 <<< Finished
 >>> Testing *Iter* using d.update(Mapping({"abcG" : %s}))
-d.update(Mapping({"abcG" : FailingIter()})):TypeError:('unable to convert FailingIter to vim structure',)
+d.update(Mapping({"abcG" : FailingIter()})):TypeError:('unable to convert FailingIter to a Vim structure',)
 d.update(Mapping({"abcG" : FailingIterNext()})):NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using d.update(Mapping({"abcG" : %s}))
@@ -911,7 +911,7 @@
 d.update((("a", {"abcF" : Mapping({"\0" : 1})}),)):TypeError:('expected string without null bytes',)
 <<< Finished
 >>> Testing *Iter* using d.update((("a", {"abcF" : %s}),))
-d.update((("a", {"abcF" : FailingIter()}),)):TypeError:('unable to convert FailingIter to vim structure',)
+d.update((("a", {"abcF" : FailingIter()}),)):TypeError:('unable to convert FailingIter to a Vim structure',)
 d.update((("a", {"abcF" : FailingIterNext()}),)):NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using d.update((("a", {"abcF" : %s}),))
@@ -938,7 +938,7 @@
 d.update((("a", Mapping({"abcG" : Mapping({"\0" : 1})})),)):TypeError:('expected string without null bytes',)
 <<< Finished
 >>> Testing *Iter* using d.update((("a", Mapping({"abcG" : %s})),))
-d.update((("a", Mapping({"abcG" : FailingIter()})),)):TypeError:('unable to convert FailingIter to vim structure',)
+d.update((("a", Mapping({"abcG" : FailingIter()})),)):TypeError:('unable to convert FailingIter to a Vim structure',)
 d.update((("a", Mapping({"abcG" : FailingIterNext()})),)):NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using d.update((("a", Mapping({"abcG" : %s})),))
@@ -950,7 +950,7 @@
 d.update((("a", Mapping({"abcG" : FailingNumber()})),)):TypeError:('long() argument must be a string or a number',)
 <<< Finished
 >>> Testing *Iter* using d.update((("a", %s),))
-d.update((("a", FailingIter()),)):TypeError:('unable to convert FailingIter to vim structure',)
+d.update((("a", FailingIter()),)):TypeError:('unable to convert FailingIter to a Vim structure',)
 d.update((("a", FailingIterNext()),)):NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using d.update((("a", %s),))
@@ -989,7 +989,7 @@
 vim.List([{"abcF" : Mapping({"\0" : 1})}]):TypeError:('expected string without null bytes',)
 <<< Finished
 >>> Testing *Iter* using vim.List([{"abcF" : %s}])
-vim.List([{"abcF" : FailingIter()}]):TypeError:('unable to convert FailingIter to vim structure',)
+vim.List([{"abcF" : FailingIter()}]):TypeError:('unable to convert FailingIter to a Vim structure',)
 vim.List([{"abcF" : FailingIterNext()}]):NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using vim.List([{"abcF" : %s}])
@@ -1016,7 +1016,7 @@
 vim.List([Mapping({"abcG" : Mapping({"\0" : 1})})]):TypeError:('expected string without null bytes',)
 <<< Finished
 >>> Testing *Iter* using vim.List([Mapping({"abcG" : %s})])
-vim.List([Mapping({"abcG" : FailingIter()})]):TypeError:('unable to convert FailingIter to vim structure',)
+vim.List([Mapping({"abcG" : FailingIter()})]):TypeError:('unable to convert FailingIter to a Vim structure',)
 vim.List([Mapping({"abcG" : FailingIterNext()})]):NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using vim.List([Mapping({"abcG" : %s})])
@@ -1028,7 +1028,7 @@
 vim.List([Mapping({"abcG" : FailingNumber()})]):TypeError:('long() argument must be a string or a number',)
 <<< Finished
 >>> Testing *Iter* using vim.List([%s])
-vim.List([FailingIter()]):TypeError:('unable to convert FailingIter to vim structure',)
+vim.List([FailingIter()]):TypeError:('unable to convert FailingIter to a Vim structure',)
 vim.List([FailingIterNext()]):NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using vim.List([%s])
@@ -1074,7 +1074,7 @@
 l[:] = [{"abcF" : Mapping({"\0" : 1})}]:TypeError:('expected string without null bytes',)
 <<< Finished
 >>> Testing *Iter* using l[:] = [{"abcF" : %s}]
-l[:] = [{"abcF" : FailingIter()}]:TypeError:('unable to convert FailingIter to vim structure',)
+l[:] = [{"abcF" : FailingIter()}]:TypeError:('unable to convert FailingIter to a Vim structure',)
 l[:] = [{"abcF" : FailingIterNext()}]:NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using l[:] = [{"abcF" : %s}]
@@ -1101,7 +1101,7 @@
 l[:] = [Mapping({"abcG" : Mapping({"\0" : 1})})]:TypeError:('expected string without null bytes',)
 <<< Finished
 >>> Testing *Iter* using l[:] = [Mapping({"abcG" : %s})]
-l[:] = [Mapping({"abcG" : FailingIter()})]:TypeError:('unable to convert FailingIter to vim structure',)
+l[:] = [Mapping({"abcG" : FailingIter()})]:TypeError:('unable to convert FailingIter to a Vim structure',)
 l[:] = [Mapping({"abcG" : FailingIterNext()})]:NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using l[:] = [Mapping({"abcG" : %s})]
@@ -1113,7 +1113,7 @@
 l[:] = [Mapping({"abcG" : FailingNumber()})]:TypeError:('long() argument must be a string or a number',)
 <<< Finished
 >>> Testing *Iter* using l[:] = [%s]
-l[:] = [FailingIter()]:TypeError:('unable to convert FailingIter to vim structure',)
+l[:] = [FailingIter()]:TypeError:('unable to convert FailingIter to a Vim structure',)
 l[:] = [FailingIterNext()]:NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using l[:] = [%s]
@@ -1145,7 +1145,7 @@
 l.extend([{"abcF" : Mapping({"\0" : 1})}]):TypeError:('expected string without null bytes',)
 <<< Finished
 >>> Testing *Iter* using l.extend([{"abcF" : %s}])
-l.extend([{"abcF" : FailingIter()}]):TypeError:('unable to convert FailingIter to vim structure',)
+l.extend([{"abcF" : FailingIter()}]):TypeError:('unable to convert FailingIter to a Vim structure',)
 l.extend([{"abcF" : FailingIterNext()}]):NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using l.extend([{"abcF" : %s}])
@@ -1172,7 +1172,7 @@
 l.extend([Mapping({"abcG" : Mapping({"\0" : 1})})]):TypeError:('expected string without null bytes',)
 <<< Finished
 >>> Testing *Iter* using l.extend([Mapping({"abcG" : %s})])
-l.extend([Mapping({"abcG" : FailingIter()})]):TypeError:('unable to convert FailingIter to vim structure',)
+l.extend([Mapping({"abcG" : FailingIter()})]):TypeError:('unable to convert FailingIter to a Vim structure',)
 l.extend([Mapping({"abcG" : FailingIterNext()})]):NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using l.extend([Mapping({"abcG" : %s})])
@@ -1184,7 +1184,7 @@
 l.extend([Mapping({"abcG" : FailingNumber()})]):TypeError:('long() argument must be a string or a number',)
 <<< Finished
 >>> Testing *Iter* using l.extend([%s])
-l.extend([FailingIter()]):TypeError:('unable to convert FailingIter to vim structure',)
+l.extend([FailingIter()]):TypeError:('unable to convert FailingIter to a Vim structure',)
 l.extend([FailingIterNext()]):NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using l.extend([%s])
@@ -1209,11 +1209,11 @@
 vim.Function("xxx_non_existent_function_xxx3", self={}):ValueError:('function xxx_non_existent_function_xxx3 does not exist',)
 vim.Function("xxx_non_existent_function_xxx4", args=[], self={}):ValueError:('function xxx_non_existent_function_xxx4 does not exist',)
 >>> FunctionNew
-vim.Function("tr", self="abcFuncSelf"):TypeError:('unable to convert str to vim dictionary',)
-vim.Function("tr", args=427423):TypeError:('unable to convert int to vim list',)
-vim.Function("tr", self="abcFuncSelf2", args="abcFuncArgs2"):TypeError:('unable to convert str to vim dictionary',)
-vim.Function(self="abcFuncSelf2", args="abcFuncArgs2"):TypeError:('unable to convert str to vim dictionary',)
-vim.Function("tr", "", self="abcFuncSelf2", args="abcFuncArgs2"):TypeError:('unable to convert str to vim dictionary',)
+vim.Function("tr", self="abcFuncSelf"):TypeError:('unable to convert str to a Vim dictionary',)
+vim.Function("tr", args=427423):TypeError:('unable to convert int to a Vim list',)
+vim.Function("tr", self="abcFuncSelf2", args="abcFuncArgs2"):TypeError:('unable to convert str to a Vim dictionary',)
+vim.Function(self="abcFuncSelf2", args="abcFuncArgs2"):TypeError:('unable to convert str to a Vim dictionary',)
+vim.Function("tr", "", self="abcFuncSelf2", args="abcFuncArgs2"):TypeError:('unable to convert str to a Vim dictionary',)
 vim.Function("tr", ""):TypeError:('function takes exactly 1 argument (2 given)',)
 >> FunctionCall
 >>> Testing StringToChars using f({%s : 1})
@@ -1232,7 +1232,7 @@
 f({"abcF" : Mapping({"\0" : 1})}):TypeError:('expected string without null bytes',)
 <<< Finished
 >>> Testing *Iter* using f({"abcF" : %s})
-f({"abcF" : FailingIter()}):TypeError:('unable to convert FailingIter to vim structure',)
+f({"abcF" : FailingIter()}):TypeError:('unable to convert FailingIter to a Vim structure',)
 f({"abcF" : FailingIterNext()}):NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using f({"abcF" : %s})
@@ -1259,7 +1259,7 @@
 f(Mapping({"abcG" : Mapping({"\0" : 1})})):TypeError:('expected string without null bytes',)
 <<< Finished
 >>> Testing *Iter* using f(Mapping({"abcG" : %s}))
-f(Mapping({"abcG" : FailingIter()})):TypeError:('unable to convert FailingIter to vim structure',)
+f(Mapping({"abcG" : FailingIter()})):TypeError:('unable to convert FailingIter to a Vim structure',)
 f(Mapping({"abcG" : FailingIterNext()})):NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using f(Mapping({"abcG" : %s}))
@@ -1271,7 +1271,7 @@
 f(Mapping({"abcG" : FailingNumber()})):TypeError:('long() argument must be a string or a number',)
 <<< Finished
 >>> Testing *Iter* using f(%s)
-f(FailingIter()):TypeError:('unable to convert FailingIter to vim structure',)
+f(FailingIter()):TypeError:('unable to convert FailingIter to a Vim structure',)
 f(FailingIterNext()):NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using f(%s)
@@ -1298,7 +1298,7 @@
 fd(self={"abcF" : Mapping({"\0" : 1})}):TypeError:('expected string without null bytes',)
 <<< Finished
 >>> Testing *Iter* using fd(self={"abcF" : %s})
-fd(self={"abcF" : FailingIter()}):TypeError:('unable to convert FailingIter to vim structure',)
+fd(self={"abcF" : FailingIter()}):TypeError:('unable to convert FailingIter to a Vim structure',)
 fd(self={"abcF" : FailingIterNext()}):NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using fd(self={"abcF" : %s})
@@ -1325,7 +1325,7 @@
 fd(self=Mapping({"abcG" : Mapping({"\0" : 1})})):TypeError:('expected string without null bytes',)
 <<< Finished
 >>> Testing *Iter* using fd(self=Mapping({"abcG" : %s}))
-fd(self=Mapping({"abcG" : FailingIter()})):TypeError:('unable to convert FailingIter to vim structure',)
+fd(self=Mapping({"abcG" : FailingIter()})):TypeError:('unable to convert FailingIter to a Vim structure',)
 fd(self=Mapping({"abcG" : FailingIterNext()})):NotImplementedError:('next',)
 <<< Finished
 >>> Testing ConvertFromPyObject using fd(self=Mapping({"abcG" : %s}))
@@ -1337,19 +1337,19 @@
 fd(self=Mapping({"abcG" : FailingNumber()})):TypeError:('long() argument must be a string or a number',)
 <<< Finished
 >>> Testing *Iter* using fd(self=%s)
-fd(self=FailingIter()):TypeError:('unable to convert FailingIter to vim dictionary',)
-fd(self=FailingIterNext()):TypeError:('unable to convert FailingIterNext to vim dictionary',)
+fd(self=FailingIter()):TypeError:('unable to convert FailingIter to a Vim dictionary',)
+fd(self=FailingIterNext()):TypeError:('unable to convert FailingIterNext to a Vim dictionary',)
 <<< Finished
 >>> Testing ConvertFromPyObject using fd(self=%s)
-fd(self=None):TypeError:('unable to convert NoneType to vim dictionary',)
+fd(self=None):TypeError:('unable to convert NoneType to a Vim dictionary',)
 fd(self={"": 1}):ValueError:('empty keys are not allowed',)
 fd(self={u"": 1}):ValueError:('empty keys are not allowed',)
 fd(self=FailingMapping()):NotImplementedError:('keys',)
 fd(self=FailingMappingKey()):NotImplementedError:('getitem:mappingkey',)
-fd(self=FailingNumber()):TypeError:('unable to convert FailingNumber to vim dictionary',)
+fd(self=FailingNumber()):TypeError:('unable to convert FailingNumber to a Vim dictionary',)
 <<< Finished
 >>> Testing ConvertFromPyMapping using fd(self=%s)
-fd(self=[]):TypeError:('unable to convert list to vim dictionary',)
+fd(self=[]):TypeError:('unable to convert list to a Vim dictionary',)
 <<< Finished
 > TabPage
 >> TabPageAttr