Newbie q about spellcheck package file types


i’ve only just started using Atom and its awesome!
but i am not very smart and i have many questions

one of them is :

i am on a mac running the latest version of yosemite
when i create a file with Atom it shows up as a ‘TextEdit Document’ in the finder and spellcheck works fine but spellcheck is ignoring plaintext files created by nvALT which show as ‘text’ files

i thought there was only one kind of text file but clearly i am mistaken. what do i enter in the spellcheck package preferences box to make it work?