Methods and apparatus for variable document printing are disclosed in which a graphical user interface is configured to allow user manipulation of layout rules associated with content containers within a template for variable document generation. One method involves laying out (626) container objects (407, 408) forming part of a template (624) intended for a variable data document. The objects each have a rectangular boundary in two-dimensional space, and the method comprises detecting an operation (628, 2800) to modify a position of at least one edge of at least one of the objects. Then, rules of association between edges of the objects having a corresponding orientation to the one edge are identified. A position of at least the one edge is then modified whilst observing the rules of association between all the correspondingly oriented edges. Finally an objective function derived from the rules of association between the correspondingly oriented edges is minimized (3009) to thereby balance a layout of the objects in at least the dimension of modification. Other methods involve maintaining the objective function for a group of edges, the addition and removal of constraints in respect of correspondingly oriented edges, the removal, addition and then removal of constraints in modifying the width of a container, the calculation of text container sizes, and the creation of tables, particularly for text containers.