多行文本框光标定位，插入字符串解决方法

多行文本框光标定位，插入字符串
一个多行文本框中有很多内容，现在要在某个位置插入字符串，如果知道光标现在所在的位置，并将字符串插入到当前位置？？

------解决方案--------------------
Option Explicit

Private Sub Command1_Click()
Dim strTest As String
strTest = "一个多行文本框中有很多内容， " & vbCrLf & "现在要在某个位置插入字符串 "
strTest = InsertStr(strTest, "内容， ", "插入的字符 ")
Debug.Print strTest
End Sub
Private Function InsertStr(strSource As String, strFind As String, strInsert As String) As String
Dim i As Long
i = InStr(1, strSource, strFind)
InsertStr = Left(strSource, i + Len(strFind) - 1) & strInsert & Right(strSource, Len(strSource) - i - Len(strFind) + 1)
End Function
------解决方案--------------------
with text1
.sellength = 0
.seltext = "插入内容 "
end with
------解决方案--------------------
晕,Left函数理解错误
Private Sub Command1_Click()
Dim s1 As String, s2 As String
s1 = Left(Text1.Text, Text1.SelStart)
s2 = Mid(Text1.Text, Text1.SelStart + 1 + Text1.SelLength)
Text1.Text = s1 & "插入的字符串 " & s2
End Sub