Methods, systems and machine-readable instructions for constraining layout variations for accommodating variable content in electronic documents are described. In one aspect, explicit logical blocks extracted from the electronic document are received. Each of the explicit logical blocks corresponds to a content region of the electronic document assigned a respective content style. Layout relationships among the explicit logical blocks are determined. Based on the layout relationships, rules constraining layout variations among implicit logical blocks to approximate the electronic document in appearance while accommodating variable content are generated. Each of the implicit logical blocks corresponds to a respective one of the explicit logical blocks and accommodates variable content having the content style assigned to the corresponding explicit logical block. The rules are stored in a machine-readable medium.