Add ParentBlock property to ContainerInline

src/Markdig.Tests/TestContainerInlines.cs

@@ -0,0 +1,41 @@
+using System;
+using Markdig.Syntax;
+using Markdig.Syntax.Inlines;
+using NUnit.Framework;
+
+namespace Markdig.Tests
+{
+    public class TestContainerInlines
+    {
+        private class MockLeafBlock : LeafBlock
+        {
+            public MockLeafBlock()
+                : base(null)
+            {
+
+            }
+        }
+
+        [Test]
+        public void CanBeAddedToLeafBlock()
+        {
+            var leafBlock1 = new MockLeafBlock();
+
+            var one = new ContainerInline();
+            Assert.Null(one.ParentBlock);
+
+            leafBlock1.Inline = one;
+            Assert.AreSame(leafBlock1, one.ParentBlock);
+
+            var two = new ContainerInline();
+            Assert.Null(two.ParentBlock);
+
+            leafBlock1.Inline = two;
+            Assert.AreSame(leafBlock1, two.ParentBlock);
+            Assert.Null(one.ParentBlock);
+
+            var leafBlock2 = new MockLeafBlock();
+            Assert.Throws<ArgumentException>(() => leafBlock2.Inline = two);
+        }
+    }
+}

src/Markdig/Syntax/Inlines/ContainerInline.cs

@@ -17,6 +17,11 @@ namespace Markdig.Syntax.Inlines
     /// <seealso cref="Inline" />
     public class ContainerInline : Inline, IEnumerable<Inline>
     {
+        /// <summary>
+        /// Gets the parent block of this inline.
+        /// </summary>
+        public LeafBlock ParentBlock { get; internal set; }
+
         /// <summary>
         /// Gets the first child.
         /// </summary>

src/Markdig/Syntax/LeafBlock.cs

@@ -16,6 +16,8 @@ namespace Markdig.Syntax
     [DebuggerDisplay("{GetType().Name} Line: {Line}, {Lines}")]
     public abstract class LeafBlock : Block
     {
+        private ContainerInline inline;
+
         /// <summary>
         /// Initializes a new instance of the <see cref="LeafBlock"/> class.
         /// </summary>
@@ -33,7 +35,30 @@ protected LeafBlock(BlockParser parser) : base(parser)
         /// <summary>
         /// Gets or sets the inline syntax tree (may be null).
         /// </summary>
-        public ContainerInline Inline { get; set; }
+        public ContainerInline Inline
+        {
+            get => inline;
+            set
+            {
+                if (value != null)
+                {
+                    if (value.Parent != null)
+                        ThrowHelper.ArgumentException("Cannot add this inline as it as already attached to another container (inline.Parent != null)");
+
+                    if (value.ParentBlock != null)
+                        ThrowHelper.ArgumentException("Cannot add this inline as it as already attached to another container (inline.ParentBlock != null)");
+
+                    value.ParentBlock = this;
+                }
+
+                if (inline != null)
+                {
+                    inline.ParentBlock = null;
+                }
+
+                inline = value;
+            }
+        }
 
         /// <summary>
         /// Gets or sets a value indicating whether <see cref="Lines"/> must be processed