Where txtfile has been defined as a file type that is opened with Vim. See VimTip1003, and try ftype /? at the command prompt.
This will cause files with no extension (e.g. "Makefile") to open automatically in Vim.
You may need to logout and log back in before this will take effect.
WARNING: Editing your Windows registry may cause unintended side effects that render your system inoperable. Although this tip has worked in the past for some people, there is no guarantee that it will work for you. Use with caution, and at your own risk.
You can also use the Windows Registry to set up the extensionless file association. For example, by importing the following registry file (adjust for correct Vim version):
Windows Registry Editor Version 5.00