diff --git a/src/Umbraco.Core/Models/Content.cs b/src/Umbraco.Core/Models/Content.cs
index 049461522d..034c9bb91d 100644
--- a/src/Umbraco.Core/Models/Content.cs
+++ b/src/Umbraco.Core/Models/Content.cs
@@ -275,57 +275,14 @@ namespace Umbraco.Core.Models
             _publishedState = PublishedState.Publishing;
         }
 
-        internal virtual void CopyValues(IContentBase other, bool published = false)
+        internal virtual void CopyValues(IContentBase other, int? languageId, string segment, bool published = false)
         {
             // clear all existing properties
-            ClearEditValues(null, null);
-
-            // copy other properties
-            var otherProperties = other.Properties;
-            foreach (var otherProperty in otherProperties)
-            {
-                var alias = otherProperty.PropertyType.Alias;
-                SetValue(alias, otherProperty.GetValue(published));
-            }
-        }
-
-        internal virtual void CopyValues(IContentBase other, int? nLanguageId, bool published = false)
-        {
-            if (!nLanguageId.HasValue)
-            {
-                CopyValues(other);
-                return;
-            }
-
-            var languageId = nLanguageId.Value;
-
-            // clear all existing properties
-            ClearEditValues(nLanguageId, null);
-
-            // copy other properties
-            var otherProperties = other.Properties;
-            foreach (var otherProperty in otherProperties)
-            {
-                var alias = otherProperty.PropertyType.Alias;
-                SetValue(alias, languageId, otherProperty.GetValue(languageId, published));
-            }
-        }
-
-        internal virtual void CopyValues(IContentBase other, int? nLanguageId, string segment, bool published = false)
-        {
-            if (segment == null)
-            {
-                CopyValues(other, nLanguageId, published);
-                return;
-            }
-
-            if (!nLanguageId.HasValue)
-                throw new ArgumentException("Cannot be null when segment is not null.", nameof(nLanguageId));
-
-            var languageId = nLanguageId.Value;
-
-            // clear all existing properties
-            ClearEditValues(nLanguageId, segment);
+            // note: use property.SetValue(), don't assign pvalue.EditValue, else change tracking fails
+            foreach (var property in Properties)
+            foreach (var pvalue in property.Values)
+                if (pvalue.LanguageId == languageId && pvalue.Segment == segment)
+                    property.SetValue(pvalue.LanguageId, pvalue.Segment, null);
 
             // copy other properties
             var otherProperties = other.Properties;
@@ -336,29 +293,13 @@ namespace Umbraco.Core.Models
             }
         }
 
-        private void ClearEditValues()
-        {
-            // clear all existing properties
-            // note: use property.SetValue(), don't assign pvalue.EditValue, else change tracking fails
-            foreach (var property in Properties)
-                foreach (var pvalue in property.Values)
-                    property.SetValue(pvalue.LanguageId, pvalue.Segment, null);
-        }
-
-        private void ClearEditValues(int? nLanguageId, string segment)
-        {
-            // clear all existing properties
-            // note: use property.SetValue(), don't assign pvalue.EditValue, else change tracking fails
-            foreach (var property in Properties)
-                foreach (var pvalue in property.Values)
-                    if (pvalue.LanguageId == nLanguageId && pvalue.Segment == segment)
-                        property.SetValue(pvalue.LanguageId, pvalue.Segment, null);
-        }
-
         internal virtual void CopyAllValues(IContentBase other, bool published = false)
         {
             // clear all existing properties
-            ClearEditValues();
+            // note: use property.SetValue(), don't assign pvalue.EditValue, else change tracking fails
+            foreach (var property in Properties)
+            foreach (var pvalue in property.Values)
+                property.SetValue(pvalue.LanguageId, pvalue.Segment, null);
 
             // copy other properties
             var otherProperties = other.Properties;
@@ -367,14 +308,8 @@ namespace Umbraco.Core.Models
                 var alias = otherProperty.PropertyType.Alias;
                 foreach (var pvalue in otherProperty.Values)
                 {
-                    // fixme can we update SetValue to accept null lang/segment and fallback?
                     var value = published ? pvalue.PublishedValue : pvalue.EditedValue;
-                    if (!pvalue.LanguageId.HasValue)
-                        SetValue(alias, value);
-                    else if (pvalue.Segment == null)
-                        SetValue(alias, pvalue.LanguageId.Value, value);
-                    else
-                        SetValue(alias, pvalue.LanguageId.Value, pvalue.Segment, value);
+                    SetValue(alias, pvalue.LanguageId, pvalue.Segment, value);
                 }
             }
         }
diff --git a/src/Umbraco.Core/Models/ContentBase.cs b/src/Umbraco.Core/Models/ContentBase.cs
index 207f54c981..a981fb3387 100644
--- a/src/Umbraco.Core/Models/ContentBase.cs
+++ b/src/Umbraco.Core/Models/ContentBase.cs
@@ -275,23 +275,39 @@ namespace Umbraco.Core.Models
         /// </summary>
         public virtual object GetValue(string propertyTypeAlias, bool published = false)
         {
-            return Properties.Contains(propertyTypeAlias) ? Properties[propertyTypeAlias].GetValue(published) : null;
+            return Properties.TryGetValue(propertyTypeAlias, out var property)
+                ? property.GetValue(published)
+                : null;
         }
 
         /// <summary>
         /// Gets the culture value of a property.
         /// </summary>
-        public virtual object GetValue(string propertyTypeAlias, int languageId, bool published = false)
+        public virtual object GetValue(string propertyTypeAlias, int? languageId, bool published = false)
         {
-            return Properties.Contains(propertyTypeAlias) ? Properties[propertyTypeAlias].GetValue(languageId, published) : null;
+            return Properties.TryGetValue(propertyTypeAlias, out var property)
+                ? property.GetValue(languageId, null, published)
+                : null;
         }
 
         /// <summary>
         /// Gets the segment value of a property.
         /// </summary>
-        public virtual object GetValue(string propertyTypeAlias, int languageId, string segment, bool published = false)
+        public virtual object GetValue(string propertyTypeAlias, string segment, bool published = false)
         {
-            return Properties.Contains(propertyTypeAlias) ? Properties[propertyTypeAlias].GetValue(languageId, segment, published) : null;
+            return Properties.TryGetValue(propertyTypeAlias, out var property)
+                ? property.GetValue(null, segment, published)
+                : null;
+        }
+
+        /// <summary>
+        /// Gets the culture+segment value of a property.
+        /// </summary>
+        public virtual object GetValue(string propertyTypeAlias, int? languageId, string segment, bool published = false)
+        {
+            return Properties.TryGetValue(propertyTypeAlias, out var property)
+                ? property.GetValue(languageId, segment, published)
+                : null;
         }
 
         /// <summary>
@@ -299,34 +315,46 @@ namespace Umbraco.Core.Models
         /// </summary>
         public virtual TPropertyValue GetValue<TPropertyValue>(string propertyTypeAlias, bool published = false)
         {
-            if (Properties.Contains(propertyTypeAlias) == false)
+            if (!Properties.TryGetValue(propertyTypeAlias, out var property))
                 return default;
 
-            var convertAttempt = Properties[propertyTypeAlias].GetValue(published).TryConvertTo<TPropertyValue>();
+            var convertAttempt = property.GetValue(published).TryConvertTo<TPropertyValue>();
             return convertAttempt.Success ? convertAttempt.Result : default;
         }
 
         /// <summary>
         /// Gets the typed culture value of a property.
         /// </summary>
-        public virtual TPropertyValue GetValue<TPropertyValue>(string propertyTypeAlias, int languageId, bool published = false)
+        public virtual TPropertyValue GetValue<TPropertyValue>(string propertyTypeAlias, int? languageId, bool published = false)
         {
-            if (Properties.Contains(propertyTypeAlias) == false)
+            if (!Properties.TryGetValue(propertyTypeAlias, out var property))
                 return default;
 
-            var convertAttempt = Properties[propertyTypeAlias].GetValue(languageId, published).TryConvertTo<TPropertyValue>();
+            var convertAttempt = property.GetValue(languageId, null, published).TryConvertTo<TPropertyValue>();
             return convertAttempt.Success ? convertAttempt.Result : default;
         }
 
         /// <summary>
         /// Gets the typed segment value of a property.
         /// </summary>
-        public virtual TPropertyValue GetValue<TPropertyValue>(string propertyTypeAlias, int languageId, string segment, bool published = false)
+        public virtual TPropertyValue GetValue<TPropertyValue>(string propertyTypeAlias, string segment, bool published = false)
         {
-            if (Properties.Contains(propertyTypeAlias) == false)
+            if (!Properties.TryGetValue(propertyTypeAlias, out var property))
                 return default;
 
-            var convertAttempt = Properties[propertyTypeAlias].GetValue(languageId, segment, published).TryConvertTo<TPropertyValue>();
+            var convertAttempt = property.GetValue(null, segment, published).TryConvertTo<TPropertyValue>();
+            return convertAttempt.Success ? convertAttempt.Result : default;
+        }
+
+        /// <summary>
+        /// Gets the typed culture+segment value of a property.
+        /// </summary>
+        public virtual TPropertyValue GetValue<TPropertyValue>(string propertyTypeAlias, int? languageId, string segment, bool published = false)
+        {
+            if (!Properties.TryGetValue(propertyTypeAlias, out var property))
+                return default;
+
+            var convertAttempt = property.GetValue(languageId, segment, published).TryConvertTo<TPropertyValue>();
             return convertAttempt.Success ? convertAttempt.Result : default;
         }
 
@@ -348,11 +376,11 @@ namespace Umbraco.Core.Models
         /// <summary>
         /// Sets the culture (draft) value of a property.
         /// </summary>
-        public virtual void SetValue(string propertyTypeAlias, int languageId, object value)
+        public virtual void SetValue(string propertyTypeAlias, int? languageId, object value)
         {
             if (value == null)
             {
-                SetValueOnProperty(propertyTypeAlias, languageId, null);
+                SetValueOnProperty(propertyTypeAlias, languageId, null, null);
                 return;
             }
 
@@ -361,9 +389,24 @@ namespace Umbraco.Core.Models
         }
 
         /// <summary>
-        /// Sets the segment (draft) value of a property.
+        /// Sets the culture+segment (draft) value of a property.
         /// </summary>
-        public virtual void SetValue(string propertyTypeAlias, int languageId, string segment, object value)
+        public virtual void SetValue(string propertyTypeAlias, string segment, object value)
+        {
+            if (value == null)
+            {
+                SetValueOnProperty(propertyTypeAlias, null, segment, null);
+                return;
+            }
+
+            // .NET magic to call one of the 'SetPropertyValue' handlers with matching signature
+            ((dynamic) this).SetPropertyValue(propertyTypeAlias, null, segment, (dynamic) value);
+        }
+
+        /// <summary>
+        /// Sets the culture+segment (draft) value of a property.
+        /// </summary>
+        public virtual void SetValue(string propertyTypeAlias, int? languageId, string segment, object value)
         {
             if (value == null)
             {
@@ -375,6 +418,16 @@ namespace Umbraco.Core.Models
             ((dynamic) this).SetPropertyValue(propertyTypeAlias, languageId, segment, (dynamic) value);
         }
 
+
+
+
+
+        // FIXME fix everything below
+
+
+
+
+
         /// <summary>
         /// Sets the neutral (draft) string value of a Property
         /// </summary>
@@ -595,30 +648,10 @@ namespace Umbraco.Core.Models
             Properties.Add(property);
         }
 
-        /// <summary>
-        /// Sets the culture (draft) value of a property.
-        /// </summary>
-        private void SetValueOnProperty(string propertyTypeAlias, int languageId, object value)
-        {
-            if (Properties.Contains(propertyTypeAlias))
-            {
-                Properties[propertyTypeAlias].SetValue(languageId, value);
-                return;
-            }
-
-            var propertyType = PropertyTypes.FirstOrDefault(x => x.Alias.InvariantEquals(propertyTypeAlias));
-            if (propertyType == null)
-                throw new InvalidOperationException($"No PropertyType exists with the supplied alias \"{propertyTypeAlias}\".");
-
-            var property = propertyType.CreateProperty();
-            property.SetValue(languageId, value);
-            Properties.Add(property);
-        }
-
         /// <summary>
         /// Sets the segment (draft) value of a property.
         /// </summary>
-        private void SetValueOnProperty(string propertyTypeAlias, int languageId, string segment, object value)
+        private void SetValueOnProperty(string propertyTypeAlias, int? languageId, string segment, object value)
         {
             if (Properties.Contains(propertyTypeAlias))
             {
@@ -649,11 +682,16 @@ namespace Umbraco.Core.Models
             return _invalidProperties.Any() == false;
         }
 
+        public virtual bool Validate(int? languageId, string segment, out IEnumerable<Property> invalidProperties)
+        {
+            // fixme etc
+        }
+
         /// <summary>
         /// Gets the properties marked as invalid during the last validation.
         /// </summary>
         [IgnoreDataMember]
-        internal IEnumerable<Property> InvalidProperties => _invalidProperties;
+        internal IEnumerable<Property> InvalidProperties => _invalidProperties; // fixme return it, don't keep it here!
 
         #endregion
 
diff --git a/src/Umbraco.Core/Models/IContentBase.cs b/src/Umbraco.Core/Models/IContentBase.cs
index 8feda0d733..ea698bff7f 100644
--- a/src/Umbraco.Core/Models/IContentBase.cs
+++ b/src/Umbraco.Core/Models/IContentBase.cs
@@ -48,7 +48,7 @@ namespace Umbraco.Core.Models
         /// </summary>
         /// <param name="propertyTypeAlias">Alias of the PropertyType</param>
         /// <returns>True if Property with given alias exists, otherwise False</returns>
-        bool HasProperty(string propertyTypeAlias);
+        bool HasProperty(string propertyTypeAlias); // fixme - what does this mean????
 
         /// <summary>
         /// Gets the neutral value of a Property
@@ -58,12 +58,17 @@ namespace Umbraco.Core.Models
         /// <summary>
         /// Gets the culture value of a Property
         /// </summary>
-        object GetValue(string propertyTypeAlias, int languageId, bool published = false);
+        object GetValue(string propertyTypeAlias, int? languageId, bool published = false);
 
         /// <summary>
         /// Gets the segment value of a Property
         /// </summary>
-        object GetValue(string propertyTypeAlias, int languageId, string segment, bool published = false);
+        object GetValue(string propertyTypeAlias, string segment, bool published = false);
+
+        /// <summary>
+        /// Gets the culture+segment value of a Property
+        /// </summary>
+        object GetValue(string propertyTypeAlias, int? languageId, string segment, bool published = false);
 
         /// <summary>
         /// Gets the typed neutral value of a Property
@@ -71,34 +76,63 @@ namespace Umbraco.Core.Models
         TPropertyValue GetValue<TPropertyValue>(string propertyTypeAlias, bool published = false);
 
         /// <summary>
-        /// Gets the typed neutral value of a Property
+        /// Gets the typed culture value of a Property
         /// </summary>
-        TPropertyValue GetValue<TPropertyValue>(string propertyTypeAlias, int languageId, bool published = false);
+        TPropertyValue GetValue<TPropertyValue>(string propertyTypeAlias, int? languageId, bool published = false);
 
         /// <summary>
-        /// Gets the typed neutral value of a Property
+        /// Gets the typed segment value of a Property
         /// </summary>
-        TPropertyValue GetValue<TPropertyValue>(string propertyTypeAlias, int languageId, string segment, bool published = false);
+        TPropertyValue GetValue<TPropertyValue>(string propertyTypeAlias, string segment, bool published = false);
 
         /// <summary>
-        /// Sets the neutral (draft) value of a Property
+        /// Gets the typed culture+segment value of a Property
+        /// </summary>
+        TPropertyValue GetValue<TPropertyValue>(string propertyTypeAlias, int? languageId, string segment, bool published = false);
+
+        /// <summary>
+        /// Sets the neutral (edited) value of a Property
         /// </summary>
         void SetValue(string propertyTypeAlias, object value);
 
         /// <summary>
-        /// Sets the culture (draft) value of a Property
+        /// Sets the culture (edited) value of a Property
         /// </summary>
-        void SetValue(string propertyTypeAlias, int languageId, object value);
+        void SetValue(string propertyTypeAlias, int? languageId, object value);
 
         /// <summary>
-        /// Sets the segment (draft) value of a Property
+        /// Sets the segment (edited) value of a Property
         /// </summary>
-        void SetValue(string propertyTypeAlias, int languageId, string segment, object value);
+        void SetValue(string propertyTypeAlias, string segment, object value);
 
         /// <summary>
-        /// Boolean indicating whether the content and its properties are valid
+        /// Sets the culture+segment (edited) value of a Property
+        /// </summary>
+        void SetValue(string propertyTypeAlias, int? languageId, string segment, object value);
+
+        /// <summary>
+        /// Gets a value indicating whether the content and its neutral properties values are valid.
         /// </summary>
-        /// <returns>True if content is valid otherwise false</returns>
         bool Validate();
+
+        /// <summary>
+        /// Gets a value indicating whether the content and its culture properties values are valid.
+        /// </summary>
+        bool Validate(int? languageId);
+
+        /// <summary>
+        /// Gets a value indicating whether the content and its segment properties values are valid.
+        /// </summary>
+        bool Validate(string segment);
+
+        /// <summary>
+        /// Gets a value indicating whether the content and its culture+segment properties values are valid.
+        /// </summary>
+        bool Validate(int? languageId, string segment);
+
+        /// <summary>
+        /// Gets a value indicating whether the content and all its properties values are valid.
+        /// </summary>
+        bool ValidateAll();
     }
 }
diff --git a/src/Umbraco.Core/Models/Property.cs b/src/Umbraco.Core/Models/Property.cs
index 557a46afd9..3e20e633dc 100644
--- a/src/Umbraco.Core/Models/Property.cs
+++ b/src/Umbraco.Core/Models/Property.cs
@@ -91,9 +91,7 @@ namespace Umbraco.Core.Models
             set
             {
                 _values = value;
-
                 _pvalue = value.FirstOrDefault(x => !x.LanguageId.HasValue && x.Segment == null);
-
                 _vvalues = value.ToDictionary(x => (x.LanguageId, x.Segment), x => x);
             }
         }
@@ -349,7 +347,7 @@ namespace Umbraco.Core.Models
         }
 
         /// <summary>
-        /// Gets a value indicating whether the (edit) neutral value is valid.
+        /// Gets a value indicating whether the (edited) neutral value is valid.
         /// </summary>
         /// <remarks>An invalid value can be saved, but only valid values can be published.</remarks>
         public bool IsValid()
@@ -358,23 +356,41 @@ namespace Umbraco.Core.Models
         }
 
         /// <summary>
-        /// Gets a value indicating whether the (edit) culture value is valid.
+        /// Gets a value indicating whether the (edited) culture value is valid.
         /// </summary>
         /// <remarks>An invalid value can be saved, but only valid values can be published.</remarks>
-        public bool IsValid(int languageId)
+        public bool IsValid(int? languageId)
         {
             return IsValid(GetValue(languageId));
         }
 
         /// <summary>
-        /// Gets a value indicating whether the (edit) segment value is valid.
+        /// Gets a value indicating whether the (edited) segment value is valid.
         /// </summary>
         /// <remarks>An invalid value can be saved, but only valid values can be published.</remarks>
-        public bool IsValue(int languageId, string segment)
+        public bool IsValue(string segment)
+        {
+            return IsValid(GetValue(segment));
+        }
+
+        /// <summary>
+        /// Gets a value indicating whether the (edited) culture+segment value is valid.
+        /// </summary>
+        /// <remarks>An invalid value can be saved, but only valid values can be published.</remarks>
+        public bool IsValue(int? languageId, string segment)
         {
             return IsValid(GetValue(languageId, segment));
         }
 
+        /// <summary>
+        /// Gets a value indicating whether all (edited) values are valid.
+        /// </summary>
+        /// <remarks>An invalid value can be saved, but only valid values can be published.</remarks>
+        public bool IsAllValid()
+        {
+            return _values.All(x => IsValid(x.EditedValue));
+        }
+
         /// <summary>
         /// Boolean indicating whether the passed in value is valid
         /// </summary>
diff --git a/src/Umbraco.Core/Models/PropertyCollection.cs b/src/Umbraco.Core/Models/PropertyCollection.cs
index 1bedf57333..9c51ddbe79 100644
--- a/src/Umbraco.Core/Models/PropertyCollection.cs
+++ b/src/Umbraco.Core/Models/PropertyCollection.cs
@@ -156,6 +156,12 @@ namespace Umbraco.Core.Models
             }
         }
 
+        public bool TryGetValue(string propertyTypeAlias, out Property property)
+        {
+            property = this[propertyTypeAlias];
+            return property != null;
+        }
+
         /// <summary>
         /// Occurs when the collection changes.
         /// </summary>