One focus of attention in mindfulness meditation has no specific focus at all. Termed “open attention” or “choiceless awareness”, the instruction for this kind of practice is simply to open the field of awareness to include mindful noticing of whatever arises.
Following a session of sitting practice we had shared, I good-naturedly teased a friend about his mismatched socks. “What’s up with that?”, I asked. Without missing a beat he answered: “Oh, that’s just choiceless awareness from the bottom up”.