So i'm not sure I understand what they're talking about but I guess they don't simply mean subtle Hi-Hat accents or phrases that you might do subconsciously ever 8th, 12 or 16th bar or over a new period or something like that? I mean every drummer that played for a long time usually have a feel for periods in music without counting bars, you feel when something changes in the music and therefor a drummer might phrase that in someway in the groove/beat without really thinking about it, i'm not talking about fills. Probably not at all what they're talking about though....