Added configuration validation for content and request handler settings.

src/Umbraco.Core/Configuration/Models/Validation/ConfigurationValidationBase.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Umbraco.Core.Configuration.Models.Validation
+{
+    public abstract class ConfigurationValidationBase
+    {
+        public bool ValidateStringIsOneOfValidValues(string configPath, string value, IEnumerable<string> validValues, out string message)
+        {
+            if (!validValues.InvariantContains(value))
+            {
+                message = $"Configuration entry {configPath} contains an invalid value '{value}', it should be one of the following: '{string.Join(", ", validValues)}'.";
+                return false;
+            }
+
+            message = string.Empty;
+            return true;
+        }
+
+        public bool ValidateStringIsOneOfEnumValues(string configPath, string value, Type enumType, out string message)
+        {
+            var validValues = Enum.GetValues(enumType).OfType<object>().Select(x => x.ToString().ToFirstLowerInvariant());
+            return ValidateStringIsOneOfValidValues(configPath, value, validValues, out message);
+        }
+    }
+}

src/Umbraco.Core/Configuration/Models/Validation/ContentSettingsValidation.cs

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+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.Extensions.Options;
+using Umbraco.Core.Macros;
+
+namespace Umbraco.Core.Configuration.Models.Validation
+{
+    public class ContentSettingsValidation : ConfigurationValidationBase, IValidateOptions<ContentSettings>
+    {
+        public ValidateOptionsResult Validate(string name, ContentSettings options)
+        {
+            string message;
+            if (!ValidateMacroErrors(options.MacroErrors, out message))
+            {
+                return ValidateOptionsResult.Fail(message);
+            }
+
+            if (!ValidateError404Collection(options.Error404Collection, out message))
+            {
+                return ValidateOptionsResult.Fail(message);
+            }
+
+            return ValidateOptionsResult.Success;
+        }
+
+        private bool ValidateMacroErrors(string value, out string message)
+        {
+            return ValidateStringIsOneOfEnumValues("Content:MacroErrors", value, typeof(MacroErrorBehaviour), out message);
+        }
+
+        private bool ValidateError404Collection(IEnumerable<ContentErrorPage> values, out string message)
+        {
+            if (values.Any(x => !x.IsValid()))
+            {
+                message = $"Configuration entry Content:Error404Collection contains one or more invalid values.  Culture and one and only one of ContentId, ContentKey and ContentXPath must be specified for each entry.";
+                return false;
+            }
+
+            message = string.Empty;
+            return true;
+        }
+    }
+}

src/Umbraco.Core/Configuration/Models/Validation/RequestHandlerSettingsValidation.cs

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+using Microsoft.Extensions.Options;
+
+namespace Umbraco.Core.Configuration.Models.Validation
+{
+    public class RequestHandlerSettingsValidation : ConfigurationValidationBase, IValidateOptions<RequestHandlerSettings>
+    {
+        public ValidateOptionsResult Validate(string name, RequestHandlerSettings options)
+        {
+            if (!ValidateConvertUrlsToAscii(options.ConvertUrlsToAscii, out var message))
+            {
+                return ValidateOptionsResult.Fail(message);
+            }
+
+            return ValidateOptionsResult.Success;
+        }
+
+        private bool ValidateConvertUrlsToAscii(string value, out string message)
+        {
+            var validValues = new[] { "try", "true", "false" };
+            return ValidateStringIsOneOfValidValues("RequestHandler:ConvertUrlsToAscii", value, validValues, out message);
+        }
+    }
+}