Improve Error handling across the board

MultiTool.Common/Constants.vb

@@ -8,6 +8,7 @@
     Public Const FUNCTION_PRICE = "PRICE"
     Public Const FUNCTION_SQL = "SQL"
     Public Const FUNCTION_FIELD = "FIELD"
+    Public Const FUNCTION_RUNNINGNUMBER = "RUNNINGNUMBER"
 
     Public Const TEMPLATE_TYPE_DATE = "xs:date"
     Public Const TEMPLATE_TYPE_INTEGER = "xs:integer"
@@ -56,17 +57,38 @@
         [Decimal]
     End Enum
 
-    Public Enum FieldError
+    Public Enum FieldErrorType
         None
         MissingValue
         AccountNotFound
         ArticleNotFound
     End Enum
 
-    Public Enum DocumentError
+    Public Class FieldError
+        Public Type As FieldErrorType
+        Public Message As String
+
+        Public Overrides Function ToString() As String
+            Return $"{Message} ({Type})"
+        End Function
+    End Class
+
+
+    Public Enum DocumentErrorType
         MandatorNotFound
+        MissingXmlAttribute
+        AttributeValidationFailed
     End Enum
 
+    Public Class DocumentError
+        Public Type As DocumentErrorType
+        Public Message As String
+
+        Public Overrides Function ToString() As String
+            Return $"{Message} ({Type})"
+        End Function
+    End Class
+
     Public Enum XmlFunction
         None = 0
         GLN = 1