暂时实现了简陋的脚本AST分析解释，后面再绑定到控件上

Serein.Script/Node/CollectionIndexNode.cs

@@ -0,0 +1,20 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Serein.Script.Node
+{
+    /// <summary>
+    /// 集合索引获取
+    /// </summary>
+    public class CollectionIndexNode : ASTNode
+    {
+        public ASTNode IndexValue { get; }
+        public CollectionIndexNode(ASTNode indexValue)
+        {
+            this.IndexValue = indexValue;
+        }
+    }
+}