这是我的程序界面,代码如下:
Private Sub Command1_Click()
x = Val(Text1.Text)
y = x \ 100: Text2.Text = y
x = x - 100 * y
y = x \ 50: Text3.Text = y
x = x - 50 * y
y = x \ 10: Text4.Text = y
x = x - 10 * y
y = x \ 5: Text5.Text = y
x = x - 5 * y
y = x \ 2: Text6.Text = y
x = x - 2 * y: Text7.Text = x
Text1.SelStart = 0
Text1.SelLength = Len(Text1.Text)
Text1.SetFocus
End Sub

Private Sub Text1_Change()
Text2.Text = ""
Text3.Text = ""
Text4.Text = ""
Text5.Text = ""
Text6.Text = ""
Text7.Text = ""
End Sub

Private Sub Form_Activate()
Text1.SetFocus
End Sub

请问:Text1.SelStart = 0
Text1.SelLength = Len(Text1.Text)
Text1.SetFocus
这三句话是什么意思?