Labelling flow object sequence

• The flow objects in a flow object sequence can be labelled with a name.
• Suppose you have a footnote paragraph inside a paragraph inside a column-set-sequence. The footnote paragraph has to attached to the foonote port of the column-set-sequence. This is achieved by labelling the footnote paragraph.
• When a labelled flow object is specified as part of the content of some flow object, the label indicates whether the flow object belongs to one of the sets of children of that flow object, and, if so, to which stream (port) it belongs.
• When a flow object is constructed and a flow object sequence is specified for the content which includes labelled flow objects that are not in one of the sets of children of the content, a flow object sequence is returned containing the constructed flow object followed by these labelled flow objects.
• An unlabelled flow object belongs to the principal stream of the flow object.