12.6.20 Side-by-side-item Flow Object Class
Use of this flow object requires the side-by-side feature.
A side-by-side-item flow object is always displayed.  It has a single principal port whose contents are displayed.  The display-size of the content is the same as the display-size of the side-by-side.  A side-by-side-item flow object shall be allowed only in a side-by-side flow object.
The following characteristics are applicable:

•  start-indent: is a length-spec specifying the indent for the edge of the area at the start in the direction of the writing-mode. The initial value is 0pt. This determines only whether adjacent side-by-side-items overlap when the side-by-side-overlap-control: characteristic of the containing side-by-side has the value indent.

•  end-indent: is a length-spec specifying the indent for the edge of the area at the end in the direction of the writing-mode. The initial value is 0pt. This determines only whether adjacent side-by-side-items overlap when the side-by-side-overlap-control: characteristic of the containing side-by-side has the value indent.

•  side-by-side-pre-align: is a symbol specifying the point that shall be used to align this item with the preceding side-by-side-item as follows:

•  start meaning the beginning edge in the placement direction of the first area produced by this side-by-side-item flow object;

•  initial meaning the placement path of the first line area produced by this side-by-side-item flow object;

•  final meaning the placement path of the last line area produced by this side-by-side-item flow object;

•  end meaning the ending edge in the placement direction of the last line area produced by this side-by-side-item flow object.

The initial value is initial.

•  side-by-side-post-align: is a symbol specifying the point that shall be used to align this item with the following side-by-side-item, in the same manner as side-by-side-pre-align:. The initial value is initial.
The side-by-side-items are positioned so that, for each side-by-side-item except the first, its side-by-side-pre-align point is aligned in the placement direction with the side-by-side-post-align point of the preceding side-by-side-item.
If side-by-side-overlap-control: has the value indent, and if the start-indent of a side-by-side-item in a side-by-side flow object is less than the difference between the display-size and the end-indent of the previous side-by-side-item in the side-by-side, then it shall be positioned after the previous side-by-side-item in the placement direction.
Any space-before: applicable to the first area produced by a side-by-side-item and any space-after: applicable to the last area produced by a side-by-side-item shall be ignored.