Fix nested lists and allow list style attribute (#198)

Fix nested ordered lists which change type not restarting (e.g. nesting a lower-alpha list in a decimal list would not restart the numbering).
Added support for parsing the <ol type="1|a|A|i|I">  attribute.

Author: Tranquilite0

src/Html2OpenXml/Expressions/Numbering/ListExpression.cs

@@ -1,4 +1,4 @@
-/* Copyright (C) Olivier Nizet https://github.com/onizet/html2openxml - All Rights Reserved
+/* Copyright (C) Olivier Nizet https://github.com/onizet/html2openxml - All Rights Reserved
  * 
  * This source is subject to the Microsoft Permissive License.
  * Please see the License.txt file for more information.
@@ -161,7 +161,15 @@ private ListContext ConcretiseInstance(ParsingContext context, int abstractNumId
         int overrideLevelIndex = 0;
         var isOrderedTag = node.NodeName.Equals("ol", StringComparison.OrdinalIgnoreCase);
         var dir = node.GetTextDirection();
-        if (!instanceId.HasValue || context.Converter.ContinueNumbering == false)
+
+        // be sure to restart to 1 any nested ordered list
+        if (currentLevel > 0 && isOrderedTag)
+        {
+            instanceId = IncrementInstanceId(context, abstractNumId, isReusable: false);
+            overrideLevelIndex = currentLevel;
+            listContext = new ListContext(listStyle, abstractNumId, instanceId.Value, currentLevel + 1, dir);
+        }
+        else if (!instanceId.HasValue || context.Converter.ContinueNumbering == false)
         {
             // create a new instance of that list template
             instanceId = IncrementInstanceId(context, abstractNumId, isReusable: context.Converter.ContinueNumbering);
@@ -176,13 +184,6 @@ private ListContext ConcretiseInstance(ParsingContext context, int abstractNumId
             instanceId = IncrementInstanceId(context, abstractNumId, isReusable: false);
             listContext =  new ListContext(listStyle, abstractNumId, instanceId.Value, 1, dir);
         }
-        // be sure to restart to 1 any nested ordered list
-        else if (currentLevel > 0 && isOrderedTag)
-        {
-            instanceId = IncrementInstanceId(context, abstractNumId, isReusable: false);
-            overrideLevelIndex = currentLevel;
-            listContext = new ListContext(listStyle, abstractNumId, instanceId.Value, currentLevel + 1, dir);
-        }
         else
         {
             return new ListContext(listStyle, abstractNumId, instanceId.Value, currentLevel + 1, dir);
@@ -215,20 +216,39 @@ private ListContext ConcretiseInstance(ParsingContext context, int abstractNumId
     private static string GetListName(IElement listNode, string? parentName = null)
     {
         var styleAttributes = listNode.GetStyles();
+        bool orderedList = listNode.NodeName.Equals("ol", StringComparison.OrdinalIgnoreCase);
         string? type = styleAttributes["list-style-type"];
 
+        if(orderedList && string.IsNullOrEmpty(type))
+        {
+            type = ListTypeToListStyleType(listNode.GetAttribute("type"));
+        }
+
         if (string.IsNullOrEmpty(type) || !supportedListTypes.Contains(type!))
         {
             if (parentName != null && IsCascadingStyle(parentName))
                 return parentName!;
 
-            bool orderedList = listNode.NodeName.Equals("ol", StringComparison.OrdinalIgnoreCase);
             type = orderedList? "decimal" : "disc";
         }
 
         return type!;
     }
 
+    /// <summary>
+    /// Map ordered list style attribute values to css list-style-type.
+    /// Valid types are "1|a|A|i|I": https://w3schools.com/tags/att_ol_type.asp
+    /// </summary>
+    private static string? ListTypeToListStyleType(string? type) => type switch
+    {
+        "1" => "decimal",
+        "a" => "lower-alpha",
+        "A" => "upper-alpha",
+        "i" => "lower-roman",
+        "I" => "upper-roman",
+        _ => null
+    };
+
     /// <summary>
     /// Resolve the <see cref="ParagraphStyleId"/> of a list element node, 
     /// based on its css class if provided and if matching.
@@ -256,4 +276,4 @@ private static bool IsCascadingStyle(string styleName)
     {
         return styleName == "decimal-tiered";
     }
-}
+}