Thanks for the git sample.
Seems like SlickEdit needs more information in order to support other types of files or ambiguous files. Right now, only the following file type extensions are supported:
.cs,.vb,.fs,.jsl,.java --> Compile
.resx,.rdlc,.txt -->EmbeddedResource
.jpg,.jpeg,.gif,.bmp,.png,.htm,.html,.dll,.exe,.wav,.avi,.mdb,.mdf,.vbs,.wsf,.css -->Content
If a file doesn't have one of the above mappings, then it is mapped to the XML element "None".