Index: generic/predefined.xotcl
===================================================================
diff -u -rf4e75c452cf99c87ad8705c954cb9548652873fa -r5a0750dc422574bc5ae91d9b58c64b8f5713d405
--- generic/predefined.xotcl	(.../predefined.xotcl)	(revision f4e75c452cf99c87ad8705c954cb9548652873fa)
+++ generic/predefined.xotcl	(.../predefined.xotcl)	(revision 5a0750dc422574bc5ae91d9b58c64b8f5713d405)
@@ -565,14 +565,16 @@
   }
   ::xotcl::RelationSlot protected method delete_value {obj prop old value} {
     if {[string first * $value] > -1 || [string first \[ $value] > -1} {
-      # string contains meta characters
+      # value contains globbing meta characters
       if {${:elementtype} ne "" && ![string match ::* $value]} {
-        # prefix string with ::, since all object names have leading ::
+        # prefix glob pattern with ::, since all object names have leading ::
         set value ::$value
       }
       return [lsearch -all -not -glob -inline $old $value]
     } elseif {${:elementtype} ne ""} {
+      # value contains no globbing meta characters, but elementtype is given
       if {[string first :: $value] == -1} {
+	# get fully qualified name
         if {![::xotcl::is $value object]} {
           error "$value does not appear to be an object"
         }
Index: generic/xotcl.c
===================================================================
diff -u -r48d5751e9aeb6a4f388f6531a9248c1847b22cae -r5a0750dc422574bc5ae91d9b58c64b8f5713d405
--- generic/xotcl.c	(.../xotcl.c)	(revision 48d5751e9aeb6a4f388f6531a9248c1847b22cae)
+++ generic/xotcl.c	(.../xotcl.c)	(revision 5a0750dc422574bc5ae91d9b58c64b8f5713d405)
@@ -6181,10 +6181,43 @@
   *clientData = (char *)ObjStr(objPtr);
   return TCL_OK;
 }
+enum stringTypeIdx {StringTypeAlnum, StringTypeAlpha, StringTypeAscii, StringTypeBoolean, StringTypeControl, 
+		    StringTypeDigit, StringTypeDouble, StringTypeFalse,StringTypeGraph, StringTypeInteger, 
+		    StringTypeLower, StringTypePrint, StringTypePunct, StringTypeSpace, StringTypeTrue, 
+		    StringTypeUpper, StringTypeWordchar, StringTypeXdigit };
+static CONST char *stringTypeOpts[] = {"alnum", "alpha", "ascii", "boolean", "control", 
+			       "digit", "double", "false", "graph", "integer", 
+			       "lower", "print", "punct", "space", "true", 
+			       "upper", "wordchar", "xdigit", NULL};
+
 static int convertToTclobj(Tcl_Interp *interp, Tcl_Obj *objPtr,  XOTclParam CONST *pPtr, ClientData *clientData) {
-  *clientData = (ClientData)objPtr;
-  return TCL_OK;
+  Tcl_Obj *objv[3];
+  int result;
+
+  if (pPtr->converterArg) {
+    /*fprintf(stderr, "convertToStringType %s (must be %s)\n", ObjStr(objPtr), ObjStr(pPtr->converterArg));*/
+
+    objv[1] = pPtr->converterArg;
+    objv[2] = objPtr;
+
+    result = XOTclCallCommand(interp, XOTE_IS, 3, objv);
+    if (result == TCL_OK) {
+      int success;
+      Tcl_GetIntFromObj(interp, Tcl_GetObjResult(interp), &success);
+      if (success == 1) {
+	*clientData = (ClientData)objPtr;
+      } else {
+	result = XOTclVarErrMsg(interp, "expected ", ObjStr(pPtr->converterArg), 
+				" but got \"", ObjStr(objPtr), "\"", NULL);
+      }
+    }
+  } else {
+    *clientData = (ClientData)objPtr;
+    result = TCL_OK;
+  }
+  return result;
 }
+
 static int convertToNothing(Tcl_Interp *interp, Tcl_Obj *objPtr,  XOTclParam CONST *pPtr, ClientData *clientData) {
   return TCL_OK;
 }
@@ -6319,6 +6352,7 @@
   paramPtr->type = typeName;
   return TCL_OK;
 }
+
 static int
 ParamOptionParse(Tcl_Interp *interp, char *option, int length, int disallowedOptions, XOTclParam *paramPtr) {
   int result = TCL_OK; 
@@ -6370,27 +6404,45 @@
     paramPtr->converterArg = Tcl_NewStringObj(option+5, length-5);
     INCR_REF_COUNT(paramPtr->converterArg);
   } else {
-    XOTclObject *paramObj;
-    Tcl_Obj *checker;
-    XOTclClass *pcl;
-    Tcl_Command cmd;
+    int i, found = -1;
+    
+    for (i=0; stringTypeOpts[i]; i++) {
+      /* Do not allow abbreviations, so the additional strlen checks
+	 for a full match */
+      if (strncmp(option, stringTypeOpts[i], length) == 0 && strlen(stringTypeOpts[i]) == length) {
+	found = i;
+	break;
+      }
+    }
+    if (found > -1) {
+      /* converter is stringType */
+      result = ParamOptionSetConverter(interp, paramPtr, "stringtype", convertToTclobj);
+      paramPtr->converterArg =  Tcl_NewStringObj(stringTypeOpts[i], -1);
+      INCR_REF_COUNT(paramPtr->converterArg);      
+    } else {
+      /* converter defined via method */
+      XOTclObject *paramObj;
+      Tcl_Obj *checker;
+      XOTclClass *pcl;
+      Tcl_Command cmd;
 
-    result = GetObjectFromObj(interp, XOTclGlobalObjects[XOTE_METHOD_PARAMETER_SLOT_OBJ], &paramObj);
-    if (result != TCL_OK)
-      return result;
+      result = GetObjectFromObj(interp, XOTclGlobalObjects[XOTE_METHOD_PARAMETER_SLOT_OBJ], &paramObj);
+      if (result != TCL_OK)
+	return result;
+      
+      checker = ParamCheckObj(interp, option, length);
+      INCR_REF_COUNT(checker);
+      cmd = ObjectFindMethod(interp, paramObj, ObjStr(checker), &pcl);
 
-    checker = ParamCheckObj(interp, option, length);
-    INCR_REF_COUNT(checker);
-    cmd = ObjectFindMethod(interp, paramObj, ObjStr(checker), &pcl);
-
-    if (cmd == NULL) {
-      fprintf(stderr, "**** could not find checker method %s defined on %s\n",
-              ObjStr(checker), objectName(paramObj));
-      paramPtr->flags |= XOTCL_ARG_CURRENTLY_UNKNOWN;
-      /* TODO: for the time being, we do not return an error here */
+      if (cmd == NULL) {
+	fprintf(stderr, "**** could not find checker method %s defined on %s\n",
+		ObjStr(checker), objectName(paramObj));
+	paramPtr->flags |= XOTCL_ARG_CURRENTLY_UNKNOWN;
+	/* TODO: for the time being, we do not return an error here */
+      }
+      result = ParamOptionSetConverter(interp, paramPtr, "usertype", convertViaCmd);
+      paramPtr->converterName = checker;
     }
-    result = ParamOptionSetConverter(interp, paramPtr, "usertype", convertViaCmd);
-    paramPtr->converterName = checker;
   }
 
   if ((paramPtr->flags & disallowedOptions)) {
Index: generic/xotclInt.h
===================================================================
diff -u -r05f4b42f7615ea410b7ac33093f5b8382ce7e8c5 -r5a0750dc422574bc5ae91d9b58c64b8f5713d405
--- generic/xotclInt.h	(.../xotclInt.h)	(revision 05f4b42f7615ea410b7ac33093f5b8382ce7e8c5)
+++ generic/xotclInt.h	(.../xotclInt.h)	(revision 5a0750dc422574bc5ae91d9b58c64b8f5713d405)
@@ -512,7 +512,7 @@
   XOTE_METHOD, XOTE_OBJECT, XOTE_SETTER, 
   XOTE_GUARD_OPTION, XOTE___UNKNOWN__, 
   /* Patly redefined Tcl commands; leave them together at the end */
-  XOTE_EXPR, XOTE_FORMAT, XOTE_INFO, XOTE_INTERP, XOTE_RENAME, XOTE_SUBST
+  XOTE_EXPR, XOTE_FORMAT, XOTE_INFO, XOTE_INTERP, XOTE_IS, XOTE_RENAME, XOTE_SUBST
 } XOTclGlobalNames;
 #if !defined(XOTCL_C)
 extern char *XOTclGlobalStrings[];
@@ -535,7 +535,7 @@
   "method", "object", "setter", 
   "-guard", "__unknown__",
   /* tcl commands */
-  "expr", "format", "info", "interp", "rename", "subst",
+  "expr", "format", "info", "interp", "::tcl::string::is", "rename", "subst",
 };
 #endif
 
Index: generic/xotclShadow.c
===================================================================
diff -u -r28acb2d7bddbbf6c82e6c516d7706f9429e05e6b -r5a0750dc422574bc5ae91d9b58c64b8f5713d405
--- generic/xotclShadow.c	(.../xotclShadow.c)	(revision 28acb2d7bddbbf6c82e6c516d7706f9429e05e6b)
+++ generic/xotclShadow.c	(.../xotclShadow.c)	(revision 5a0750dc422574bc5ae91d9b58c64b8f5713d405)
@@ -131,6 +131,7 @@
 #endif
     rc |= XOTclReplaceCommand(interp, XOTE_FORMAT,   0, initialized);
     rc |= XOTclReplaceCommand(interp, XOTE_INTERP,   0, initialized);
+    rc |= XOTclReplaceCommand(interp, XOTE_IS,       0, initialized);
 
     /* for the following commands, we have to add our own semantics */
     rc |= XOTclReplaceCommand(interp, XOTE_RENAME,   XOTcl_RenameObjCmd, initialized);
Index: tests/parameters.xotcl
===================================================================
diff -u -r48d5751e9aeb6a4f388f6531a9248c1847b22cae -r5a0750dc422574bc5ae91d9b58c64b8f5713d405
--- tests/parameters.xotcl	(.../parameters.xotcl)	(revision 48d5751e9aeb6a4f388f6531a9248c1847b22cae)
+++ tests/parameters.xotcl	(.../parameters.xotcl)	(revision 5a0750dc422574bc5ae91d9b58c64b8f5713d405)
@@ -12,7 +12,6 @@
 #######################################################
 Test case valuecheck
 Test parameter count 10000
-#Test parameter count 10
 
 Object create o1
 Class create C -parameter {a {b:boolean} {c 1}}
@@ -34,6 +33,11 @@
 # do not allow "currently unknown" user defined types in valuecheck
 ? {::xotcl::valuecheck in1 aaa} {invalid value constraints "in1"}
 
+? {::xotcl::valuecheck lower c} 1 "lower case char"
+? {::xotcl::valuecheck lower abc} 1 "lower case chars"
+? {::xotcl::valuecheck lower Abc} 0 "no lower case chars"
+? {string is lower abc} 1 "tcl command 'string is lower'"
+
 #
 # parameter options
 #   required
@@ -55,6 +59,7 @@
 #  method             NO         YES        YES   YES     NO        NO/POSSIBLE    YES
 #
 #  relation           NO         YES        NO    YES     NO           NO          YES
+#  stringtype         YES        YES        NO    NO      YES          YES         YES
 #
 #  switch             NO         NO         NO    NO      NO           YES         YES
 #  integer            YES        YES        NO    NO      YES          YES         YES    
@@ -226,6 +231,14 @@
     {Parameter option 'relation' not allowed} \
     "don't allow relation option as method parameter"
 
+? {D method foo {a:double} {return $a}} \
+    {::xotcl::classes::D::foo} \
+    "allow 'string is XXXX' for argument checking"
+? {d1 foo 1} 1 "check int as double"
+? {d1 foo 1.1} 1.1 "check double as double"
+? {d1 foo 1.1a} {expected double but got "1.1a"} "check non-double as double"
+? {D info method parameter foo} a:double
+
 #######################################################
 # non required positional arguments
 #######################################################
@@ -245,7 +258,7 @@
 ? {d1 foo 1} "1-0-0-1" "omit optional arguments"
 
 #######################################################
-# non required positional arguments
+# multivalued arguments
 #######################################################
 Test case multivalued
 Object create o
@@ -581,6 +594,7 @@
 C create c1 -mixin M
 Object create o
 
+puts stderr =====
 Class create ParamTest -parameter {
   o:object
   c:class
@@ -589,6 +603,8 @@
   m:metaclass
   mix:mixin,arg=M
   b:baseclass
+  u:upper
+  us:upper,multivalued
   {x:object,multivalued {o}}
 }
 
@@ -604,6 +620,8 @@
 ? {parameterFromSlot ParamTest d1} "d1:object,type=::C"
 ? {parameterFromSlot ParamTest mix} "mix:mixin,arg=M"
 ? {parameterFromSlot ParamTest x} "x:object,multivalued o"
+? {parameterFromSlot ParamTest u} "u:upper"
+? {parameterFromSlot ParamTest us} "us:upper,multivalued"
 
 ? {ParamTest create p -o o} ::p
 ? {ParamTest create p -o xxx} \
@@ -621,6 +639,10 @@
 ? {ParamTest create p -d o} \
     {expected object of type ::C but got "o"} \
     "o not of type ::C"
+? {ParamTest create p -u A} ::p
+? {ParamTest create p -u c1} {expected upper but got "c1"}
+? {ParamTest create p -us {A B}} ::p
+? {p us add C end} "A B C"
 
 # TODO: naming "type" and "mixin" not perfect.
 #       maybe "type" => "hastype"