  In a recent article (P.Wochner et al., PNAS (2009)) x-ray scattering
intensity correlations around a ring, in the speckle diffraction pattern of a
colloidal glass, were shown to display a remarkable ~ cos(n $\phi$) dependence
on the angular coordinate $\phi$ around the ring, with integer index n
depending on the magnitude of the scattering wavevector. With an analytical
derivation that preserves full generality in the Fraunhofer diffraction limit,
we clarify the relationship of this result to previous x-ray studies of
bond-orientation order, and provide a sound basis to the statement that the
angular intensity correlations deliver information on local bond arrangements
in a disordered (or partially ordered) system. We present a detailed analysis
of the angular cross-correlation function and show its applicability for
studies of wide range of structural properties of disordered systems, from
local structure to spatial correlations between distant structural elements.
