Synchronizing flow objects

• Constrain relative position of flow objects in different streams.
• For example, constrain position of footnotes/floating figures/sidenodes relative to reference.
• For example, constrain parallel translations to start each paragraph at same vertical point.
• When constructing flow object tree, can specify that flow objects are part of a synchronization set
• Each synchronization set must have synchronizing flow object that contains either directly or indirectly all members of synchronization set. Each stream of synchronizing flow object can contain at most one member of synchronization set.
• For synchronization sets with two members, can constrain placement of members so that number of pages/spread/columns between them is between specified limits.
• For synchronization sets with arbitrarily many members, can constrain members of synchronization set to have same position in column-set area