Vftool syntax file is used to customize the language-specific features, like 'Line comment symbols for Comment/Uncomment functions', 'Language keywords for auto-complete', etc.

VFTool syntax file format is compatible with the wordfile of the popular text editor Ultraedit(http://www.altraedit.com). You can find more information about Ultraedit wordfiles at:
http://www.ultraedit.com/index.php?name=Content&pa=showpage&pid=40#wordfiles

If you want vftool to support more languages or your own lanuage, you just need to put the syntax files into [vftool]/syntax/, or you could simply copy the existing Ultraedit wordfiles to this directory.

Note:

Vftool Syntax filse have to be put under [vftool]/syntax/. ([vftool] is the directory where you installed Vftool.),
and they have to use the extension names as 'txt'.