Auto complete text box in excel VBA - visual-studio-2010

Question

I am creating a excel sheet that would autocomplete a text based on the text present in a particular column. After trying to make one myself unsuccessfully, I was looking online for sample codes that I could modify and incorporate in my program. (and not plagiarize)
I downloaded Workbook1.xls from http://www.ozgrid.com/forum/showthread.php?t=144438
The code is
Option Explicit
Dim ufEventsDisabled As Boolean
Dim autoCompleteEnabled As Boolean
Dim oRange As Range
Private Sub TextBox1_Change()
If ufEventsDisabled Then Exit Sub
If autoCompleteEnabled Then Call myAutoComplete(TextBox1)
End Sub
Sub myAutoComplete(aTextBox As MSForms.TextBox)
Dim RestOfCompletion As String
On Error GoTo Halt
With aTextBox
If .SelStart + .SelLength = Len(.Text) Then
RestOfCompletion = Mid(oRange.Cells(1, 1).AutoComplete(.Text), Len(.Text) + 1)
ufEventsDisabled = True
.Text = .Text & RestOfCompletion
.SelStart = Len(.Text) - Len(RestOfCompletion)
.SelLength = Len(RestOfCompletion)
End If
End With
Halt:
ufEventsDisabled = False
On Error GoTo 0
End Sub
Private Sub TextBox1_AfterUpdate()
Dim strCompleted As String
With TextBox1
strCompleted = oRange.AutoComplete(.Text)
If LCase(strCompleted) = LCase(.Text) Then
ufEventsDisabled = True
.Text = strCompleted
ufEventsDisabled = False
End If
End With
End Sub
Private Sub TextBox1_Enter()
Set oRange = ThisWorkbook.Sheets("Sheet1").Range("f4")
End Sub
Private Sub TextBox1_KeyDown(ByVal KeyCode As MSForms.ReturnInteger, ByVal Shift As Integer)
autoCompleteEnabled = KeyCode <> vbKeyBack
autoCompleteEnabled = ((vbKey0 <= KeyCode) And (KeyCode <= vbKeyZ))
End Sub
Private Sub CommandButton1_Click()
Unload Me
End Sub
Private Sub UserForm_Click()
End Sub
If you'd notice the line RestOfCompletion = Mid(oRange.Cells(1, 1).AutoComplete(.Text), Len(.Text) + 1), I was wondering what AutoComplete is doing here. Its not a in built function and is not defined anywhere. Still the code runs fine. I am very curious.
Thanks

Answer 1

The .AutoComplete is a function of the Range object - it is based on passing the text to a range that exists elsewhere on the sheet.
You can see the documentation on this function here:
http://msdn.microsoft.com/en-us/library/bb209667(v=office.12).aspx
The myAutoComplete function handles the finding of the autocomplete data against the range if it exists, and the other pieces in the code are for highlighting the correct piece of text.