Table of contents

Appendices

4.4 Block-areas

Block-areas have several traits which typically affect the placement of their children. The line-height is used in line placement calculations. The line-stacking-strategy trait controls what kind of allocation is used for descendant line-areas and has an enumerated value (either font-height, max-height, or line-height). This is all rigorously described below. All areas have these traits, but they only have relevance for areas which have stacked line-area children.

The space-before and space-after traits determine the distance between the block-area and surrounding block-areas.

A block-area which is not a line-area typically has its size in the inline-progression-direction determined by its start-indent and end-indent and by the size of its nearest ancestor reference-area. A block-area which is not a line-area must be properly stacked (as defined in [area-stackblock] below) unless otherwise specified in the description of its generating formatting object. In this case it its block-progression-dimension will be subject to constraints based on the block-progression-dimensions and space-specifiers of its descendants. See [bpd-slack]

Stacked Block-areas[top]

Block-area children of an area are typically stacked in the block-progression-direction within their parent area, and this is the default method of positioning block-areas. However, formatting objects are free to specify other methods of positioning child areas of areas which they generate, for example list-items or tables.

For a parent area P whose children are block-areas, P is defined to be properly stacked if all of the following conditions hold:

1. For each block-area B which is a descendant of P, the following hold:

   • the before-edge and after-edge of its allocation-rectangle are parallel to the before-edge and after-edges of the content-rectangle of P,

   • the start-edge of its allocation-rectangle is parallel to the start-edge of the content-rectangle of R (where R is the closest ancestor reference-area of B), and offset from it inward by a distance equal to the block-area's start-indent plus its start-intrusion-adjustment (as defined below), minus its border-start, padding-start, and space-start values, and

   • the end-edge of its allocation-rectangle is parallel to the end-edge of the content-rectangle of R, and offset from it inward by a distance equal to the block-area's end-indent plus its end-intrusion-adjustment (as defined below), minus its border-end, padding-end, and space-end values.

   

   Content Rectangle of Reference Area

   NOTE: 

   The notion of indent is intended to apply to the content-rectangle, but the constraint is written in terms of the allocation-rectangle, because as noted earlier ( [area-geo] ) the edges of the content-rectangle may not correspond to like-named edges of the allocation-rectangle.

   The start-intrusion-adjustment and end-intrusion-adjustment are traits used to deal with intrusions from floats in the inline-progression-direction.

2. For each pair of normal areas B and B' in the subtree below P, if B and B' have a block-stacking constraint S and B is not empty (see [area-stackcon] ), then the distance between the adjacent edges of B and B' is consistent with the constraint imposed by the resolved values of the space-specifiers in S.

   

   Example. In the diagram, if area A has a space-after value of 3 points, B a space-before of 1 point, and C a space-before of 2 points, all with precedence of force, and with zero border and padding, then the constraints will place B's allocation-rectangle 4 points below that of A, and C's allocation-rectangle 6 points below that of A. Thus the 4-point gap receives the background color from P, and the 2-point gap before C receives the background color from B.

Intrusion Adjustments[top]

Intrusion adjustments (both start- and end-) are defined to account for the indentation that occurs as the result of side floats.

If A and B are areas which have the same nearest reference area ancestor, then A and B are defined to be inline-overlapping if there is some line parallel to the inline-progression-direction, which intersects both the allocation-rectangle of A and the allocation-rectangle of B.

If A is an area of class xsl-side-float with float="start", and B is a block-area, and A and B have the same nearest reference area ancestor, then A is defined to encroach upon B if A and B are inline-overlapping and the start-indent of B is less than the sum of the start-indent of A and the inline-progression-dimension of A. The start-encroachment of A on B is then defined to be amount by which the start-indent of B is less than the sum of the start-indent of A and the inline-progression-dimension of A.

If A is an area of class xsl-side-float with float="end", and B is a block-area, and A and B have the same nearest reference area ancestor, then A is defined to encroach upon B if A and B are inline-overlapping and the end-indent of B is less than the sum of the end-indent of A and the inline-progression-dimension of A. The end-encroachment of A on B is then defined to be amount by which the end-indent of B is less than the sum of the end-indent of A and the inline-progression-dimension of A.

If B is a block-area which is not a line-area, then its local-start-intrusion-adjustment is computed as the maximum of the following lengths:

1. zero;

2. if the parent of B is not a reference area: the start-intrusion-adjustment of the parent of B; and

3. if B has float-displace="block", then for each area A of class xsl-side-float with float="start" such that the generating formatting object of A is not a descendant of the generating formatting object of B, and such that A encroaches upon some line-area child of B: the start-encroachment of A on B; and

4. if B has float-displace = "block", then for each area A of class xsl-side-float with float="start" such that A and B are inline-overlapping, and for each block-area ancestor B' of B which is a descendant of the nearest reference area ancestor of B, such that A encroaches on a line-area child of B': the start-encroachment of A on B'.

The start-intrusion-adjustment of a block-area B is then defined to be the maximum of the local-start-intrusion-adjustments of the normal block-areas generated and returned by the generating formatting object of B.

If L is a line-area, then its start-intrusion-adjustment is computed as the maximum of the following lengths:

1. the start-intrusion-adjustment of the parent of L;

2. for each area A of class xsl-side-float with float="start" such that A encroaches upon L: the start-encroachment of A on L; and

3. if the parent of L has float-displace = "indent", then for each area A of class xsl-side-float with float="start" such that A and L are inline-overlapping, and for each block-area ancestor B' of L which is a descendant of the nearest reference area ancestor of L, such that A encroaches on some line-area child L' of B': the start-encroachment of A on B'.

The end-intrusion-adjustment for a block-area is computed in a precisely analogous manner. That is:

If B is a block-area which is not a line-area, then its local-end-intrusion-adjustment is computed as the maximum of the following lengths:

1. zero;

2. if the parent of B is not a reference area: the end-intrusion-adjustment of the parent of B; and

3. if B has float-displace="block", then for each area A of class xsl-side-float with float="end" such that the generating formatting object of A is not a descendant of the generating formatting object of B, and such that A encroaches upon some line-area child of B: the end-encroachment of A on B; and

4. if B has float-displace = "block", then for each area A of class xsl-side-float with float="end" such that A and B are inline-overlapping, and for each block-area ancestor B' of B which is a descendant of the nearest reference area ancestor of B, such that A encroaches on a line-area child of B': the end-encroachment of A on B'.

The end-intrusion-adjustment of a block-area B is then defined to be the maximum of the local-end-intrusion-adjustments of the normal block-areas generated and returned by the generating formatting object of B.

If L is a line-area, then its end-intrusion-adjustment is computed as the maximum of the following lengths:

1. the end-intrusion-adjustment of the parent of L;

2. for each area A of class xsl-side-float with float="end" such that A encroaches upon L: the end-encroachment of A on L; and

3. if the parent of L has float-displace = "indent", then for each area A of class xsl-side-float with float="end" such that A and L are inline-overlapping, and for each block-area ancestor B' of L which is a descendant of the nearest reference area ancestor of L, such that A encroaches on some line-area child L' of B': the end-encroachment of A on B'.