text folder of any Glyph folder contains all the text source files used to produce a document. Although there are no restrictions on the extension of the files in this folder, you may want to use
.glyph, especially if Vim is your favorite text editor.
The reason is simple: a Glyph syntax file is available on vim.org. Although not essential, syntax highlighting does help when editing Glyph files.
If you use TextMate, you may want to check out Eric Givens’ Glyph TextMate Bundle.