diff --git a/lua.lyx b/lua.lyx
index 08b8ae58..fba57840 100644
--- a/lua.lyx
+++ b/lua.lyx
@@ -513,7 +513,44 @@ If conversion is successful, returns (true, {converted-string}).
 \end_layout
 
 \begin_layout Itemize
-If conversion was unsuccessful, returns (
+If conversion was unsuccessful, returns (false, {converted-part}, {unconverted-b
+ytes}, {error}).
+ The following errors are defined:
+\end_layout
+
+\begin_deeper
+\begin_layout Itemize
+INVALID: Invalid byte sequence in input
+\end_layout
+
+\begin_layout Itemize
+INCOMPLETE: The input is cut of in middle of multi-byte sequence
+\end_layout
+
+\begin_layout Itemize
+INTERNALERR: Internal errror
+\end_layout
+
+\end_deeper
+\begin_layout Subsection
+identify_class: Identify class of object
+\end_layout
+
+\begin_layout Itemize
+Syntax: string identify_class(userdata object)
+\end_layout
+
+\begin_layout Standard
+Identifies the class of userdata <object>, if possible.
+ If no identification is possible, returns 
+\begin_inset Quotes eld
+\end_inset
+
+unknown
+\begin_inset Quotes erd
+\end_inset
+
+.
 \end_layout
 
 \begin_layout Standard
diff --git a/lua.pdf b/lua.pdf
index db0fc6f2..d917a589 100644
Binary files a/lua.pdf and b/lua.pdf differ
diff --git a/src/lua/core.cpp b/src/lua/core.cpp
index 109acd6b..a1c4874f 100644
--- a/src/lua/core.cpp
+++ b/src/lua/core.cpp
@@ -67,8 +67,14 @@ namespace
 		}
 	}
 
-	lua::fnptr lua_tostringx(lua_func_misc, "tostringx", [](lua::state& L, const std::string& fname) ->
-		int {
+	lua::fnptr lua_ctype(lua_func_misc, "identify_class", [](lua::state& L, const std::string& fname) -> int {
+		if(L.type(1) != LUA_TUSERDATA)
+			return 0;
+		L.pushlstring(try_recognize_userdata(L, 1));
+		return 1;
+	});
+
+	lua::fnptr lua_tostringx(lua_func_misc, "tostringx", [](lua::state& L, const std::string& fname) -> int {
 		std::set<const void*> tmp2;
 		std::string y = luavalue_to_string(L, 1, tmp2, false);
 		L.pushlstring(y.c_str(), y.length());