12.6.9 Sideline Flow Object Class
Use of this flow object requires the sideline feature.
A sideline flow object is used to contain flow objects that have an attachment area (see section 12.3.4, Attachment Areas) consisting of a line parallel to the placement direction. A sideline flow object has a single principal port which can contain both inlined and displayed flow objects.  For each display area produced by its content, the sideline flow object adds an attachment.  For each inline area produced by its content, the sideline flow object annotates that area so as to cause the paragraph in which the flow object occurs to add an attachment area to the line in which that inline area occurs.

NOTE 78

Sidelines are often used to mark changes.
This is illustrated in Figure 14, Attachment Areas.
A sideline flow object has the following characteristics:

•  sideline-side: is one of the symbols start, end, both, spread-inside, spread-outside, page-inside, or page-outside, specifying the side of the line area for the sideline attachment.  A value of spread-inside or spread-outside is allowed only if the flow object has an ancestor of class page-sequence.  A value of page-inside or page-outside is allowed only if the flow object has an ancestor of column-set-sequence.  A value of both means that there shall be a sideline attachment on both sides of the line area containing the text.

•  sideline-sep: is a length-spec specifying the separation for the sideline attachment. A negative value is allowed.

•  color: is an object of type color that specifies the color in which the flow object's marks should be made. The initial value is the default color in the Device Gray color space.

•  layer: is an integer specifying the layer of the marks of the areas resulting from the flow object.  An area shall be imaged after any area whose layer has a lower value. The initial value is 0.

•  line-cap: is one of the symbols butt, round, or square specifying the cap style for the line. The initial value is butt.

•  line-dash: is a list of one or more lengths that specifies the dash pattern of the line.  The first length specifies the number component of the CurrentDashPattern graphics state variable in ISO/IEC 10180.  The remaining lengths specify the vector component of the CurrentDashPattern graphics state variable. The initial value is a list containing the length 0pt.

•  line-thickness: is a length that specifies the thickness of the line or lines. The initial value is 1pt.

•  line-repeat: is a strictly positive integer that specifies the number of parallel lines to be drawn.  For example, a value of 2 indicates a double line. The initial value is 1.

•  line-sep: is a length that gives the distance between the centers of parallel lines. The initial value is 1pt.
Sidelines on consecutive areas in a single area container which have no space between them should be drawn as a single line.