  The structure of QCD vacuum can be studied from first principles using
lattice-regularized theory. This line of research entered a qualitatively new
phase recently, wherein the space-time structure (at least for some quantities)
can be directly observed in configurations dominating the QCD path integral,
i.e. without any subjective processing of typical configurations. This approach
to QCD vacuum structure does not rely on any proposed picture of QCD vacuum but
rather attempts to characterize this structure in a model-independent manner,
so that a coherent physical picture of the vacuum can emerge when such unbiased
numerical information accumulates to a sufficient degree. An important part of
this program is to develop a set of suitable quantitative characteristics
describing the space-time structure in a meaningful and physically relevant
manner. One of the basic pertinent issues here is whether QCD vacuum dynamics
can be understood in terms of localized vacuum objects, or whether such objects
behave as inherently global entities. The first direct studies of vacuum
structure strongly support the latter. In this paper, we develop a formal
framework which allows to answer this question in a quantitative manner. We
discuss in detail how to apply this approach to Dirac eigenmodes and to basic
scalar and pseudoscalar composites of gauge fields (action density and
topological charge density). The approach is illustrated numerically on overlap
Dirac zeromodes and near-zeromodes. This illustrative data provides direct
quantitative evidence supporting our earlier arguments for the global nature of
QCD Dirac eigenmodes.
