1. A graphical user interface stored on a machine-readable medium for facilitating human interaction with a database of legal documents, the interface comprising: a first interface screen including: a first data window for displaying one or more portions of a first legal document containing one or more citations to other legal documents; and a first control interface adjacent the data window, the first control interface having first user-selectable means for indicating before selection whether the first legal document includes at least one portion having compromised legal authority and for invoking after selection display of a second interface screen, wherein the second interface screen comprises: a second data window for displaying one or more citations to other legal documents that reference the first legal document or other legal documents that the first legal document is otherwise related to; and a second control interface adjacent the second data window, the second control interface having second user-selectable means for affecting the number or type of citations displayed in the second data window; and third user-selectable means for invoking display of a third interface screen, wherein the third interface screen comprises: a third data window for displaying in a first mode one or more headnotes associated with the first legal document and for displaying in a second mode one or more subject-matter classifications associated with the first legal document; and a third control interface adjacent the third data window the third control interface including: fourth user-selectable means for switching the third data window between the first and second modes; fifth user-selectable means for selecting one or more headnotes; and sixth user-selectable means for selecting one or more legal subject-matter classifications; and seventh user-selectable means for re-invoking display of the second control screen, with the second display window responsive to the fifth or sixth user-selectable means to limit display of citations based on the selected headnotes or the selected subject-matter classifications.