Separating multiple search criteria with a comma - vba

Question

I am using an Access form to search a table using different textboxes, i.e. Title, Author, Date etc.
Right now I use this code to perform the search, and update a subform with the results:
Private Sub sFindData(strTitle As String, dtmDate As String, strAuthor As String)
On Error Go to E_Handle
Dim strSQL As String
If Len(strTitle) > 0 Then
strSQL = strSQL & " AND Title LIKE '*" & strTitle & "*' "
End If
If (IsDate(dtmDate)) Then
strSQL = strSQL & " AND DocumentDate=" & Format(Me!txtDate, "\#mm\/dd\/yyyy\#")
End If
If Len(strAuthor) > 0 Then
strSQL = strSQL & " AND Author LIKE '*" & strAuthor & "*' "
End If
If Left(strSQL, 4) = " AND" Then
strSQL = " WHERE " & Mid(strSQL, 5)
End If
strSQL = "SELECT Title, DocumentDate, Author FROM tblDocument" & strSQL
Me!sSubTable.Form.RecordSource = strSQL
sExit:
On Error Resume Next
Exit Sub
E_Handle:
MsgBox Err.Description & VbCrLf & VbCrLf & Err.Source & VbCrLf & VbCrLf & "sFindData", vbOKOnly + vbCritical, "Error: " & Err.Number
And I use this code to call sFindData through textboxes on the form:
Private Sub txtTitle_Change()
Call sFindData(Nz(Me!txtTitle.Text, ""), Nz(Me!txtDate, #12/31/2099#), Nz(Me!txtAuthor, "")
End Sub
I have a Change Sub for every textbox in the main form, each bound to its own field through the same code shown above.
My problem is, I sometimes need to search multiple criteria of the same type (two different document titles for example), and I want to be able to do it in one field if possible, i.e. separate the two criteria with a comma (Title#1, Title#2) and have the code search both of these criteria and show the results on the subform
Thanks in advance