Can someone explain what this code is doing line by line?

 Public Function FastCut(s As String)
       'returns first n chars which fit pattern *nn?
       Dim x As Long
       Dim flag As Boolean
       Dim a As String
       For x = 1 To Len(s)
           a = a & Mid(s, x, 1)
           If IsNumeric(Right(a, 1)) Then flag = True
           If (flag And Not IsNumeric(Right(a, 1))) Then Exit For
       Next x
       FastCut = a

       End Function