为什么XML列是灰色的？

Question

为什么XML专栏不允许我放入任何内容并且显示为灰色，我可以填充其他列ID A或ID BI可以添加值但是使用Xml它不会让我添加任何内容，甚至＆ ＃34; <element>＆＃34; ？

创建这样的表，

USE [DBNAME]
GO

DROP TABLE [dbo].[TableName]
GO

SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

CREATE TABLE [dbo].[TableName](
    [Id] [int] IDENTITY(1,1) NOT NULL,
    [ID_A] [int] NULL,
    [ID_B] [int] NULL,
    [Xml] [xml] NULL,
 CONSTRAINT [PK_TableName] PRIMARY KEY CLUSTERED 
(
    [Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 80) ON [PRIMARY],
 CONSTRAINT [IX_TableName] UNIQUE NONCLUSTERED 
(
    [ID_A] ASC,
    [ID_B] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 80) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]

GO