Ever since I took a seminar under Joe Grimes at Cornell in 1971 on “Discourse Analysis” [see #008 and #009], I have been gung ho on what I call “Discourse Particles”. 
In my dissertation (#019 on our website), you will note that I treated them in discussions from 4.10.2 [p.157] through 4.10.4 [p.161] and in Table 38 [p.160]