21. In a computer program having data structures included on a computer readable medium for displaying in display screen windows documents, each comprising at least one display screen page containing visual information including text, the improvement comprising: means for determining a significant page edge, means for sampling the visual information density at a sequence of horizontal positions in a medial direction with respect to said more significant page edge, means for comparing each sequential sample of said visual information density to a selected density level, and means responsive to said comparing means for positioning said visual information in said window with respect to a reference margin determined by a sample of said visual information attaining said selected density level.
22. The computer program of claim 21 further including: means for storing digital representations of said screen pages, and wherein said means for sampling said visual information density samples said stored representations.