While many sources call Zhan Zhuang "standing meditation," probably to distinguish it from simple standing in one spot, I try to
avoid looking at it as a standing version of other types of meditation (concentration, insight) that call for specific mental practices not addressed in Zhan Zhuang practice. I think that standing while meditating might distract from those practices.
Meditation is really mentally-focused, doing head stuff that isn't called for in Zhan Zhuang. ZZ is really
body-focused, in my opinion, where we note changes happening in how we stand, how we sense our bodies and their components, and how we can help them interact together, more efficiently.
However, I think that
mindfulness can enhance Zhan Zhuang practice, allowing for an unbiased, non-judgmental examination and awareness of the changes happening (at the present moment) during standing practice. Mindfulness doesn't have to be practiced sitting down in a monastery: instead, it's an approach to how we sense things around us: unbiased, non-judgmental, non-evaluating, current. Mindfulness can be practiced while doing anything: eating, working, walking, cleaning. It's also called paying "bare attention" to what's at hand, without letting our mind wander to judge the thing, to compare it to things not at hand, to "multi-task" ... that sort of thing.
Mindfulness - Wikipedia, the free encyclopedia
This article defines mindfulness as "a moment-to-moment awareness of one's experience without judgment."
http://www.apa.org/monitor/2012/07-08/ce-corner.aspx
Here's an article on concentration meditation vs. mindfulness:
http://www.apa.org/monitor/2012/07-08/ce-corner.aspx