Table of contents

Appendices

4.7 Ordering Constraints

General Ordering Constraints[top]

A subset S of the areas returned to a formatting object is called properly ordered if the areas in that subset have the same order as their generating formatting objects. Specifically, if A1 and A2 are areas in S, returned by child formatting objects F1 and F2 where F1 precedes F2, then A1 must precede A2 in the pre-order traversal order of the area tree. If F1 equals F2 and A1 is returned prior to A2, then A1 must precede A2 in the pre-order-traversal of the area tree.

For each formatting object F and each area-class C, the subset consisting of the areas returned to F with area-class C must be properly ordered, except where otherwise specified.

Line-building[top]

This section describes the ordering constraints that apply to formatting an fo:block or similar block-level object.

A block-level formatting object F which constructs lines does so by constructing block-areas which it returns to its parent formatting object, and placing normal areas and/or anchor areas returned to F by its child formatting objects as children of those block-areas or of line-areas which it constructs as children of those block-areas.

For each such formatting object F, it must be possible to form an ordered partition P consisting of ordered subsets S1, S2, ..., Sn of the normal areas and anchor areas returned by the child formatting objects, such that the following are all satisfied:

1. Each subset consists of a sequence of inline-areas, or of a single block-area.

2. The ordering of the partition follows the ordering of the formatting object tree. Specifically, if A is in Si and B is in Sj with i < j, or if A and B are both in the same subset Si with A before B in the subset order, then either A is returned by a preceding sibling formatting object of B, or A and B are returned by the same formatting object with A being returned before B.

3. The partitioning occurs at legal line-breaks. Specifically, if A is the last area of Si and B is the first area of Si+1, then the rules of the language and script in effect must permit a line-break between A and B, within the context of all areas in Si and Si+1.

4. Forced line-breaks are respected. Specifically, if A is the glyph-area generated by a fo:character whose Unicode character is U+000A, then A must be the last area in its containing subset Si.

5. The partition follows the ordering of the area tree, except for certain glyph substitutions and deletions. Specifically, if B1, B2, ..., Bp are the normal child areas of the area or areas returned by F, (ordered in the pre-order traversal order of the area tree) then there is a one-to-one correspondence between these child areas and the partition subsets (i.e., n = p), and for each i,

   • if Si consists of a single block-area then Bi is that block-area, and

   • if Si consists of inline-areas then Bi is a line-area whose child areas are the same as the inline-areas in Si, and in the same order, except that where the rules of the language and script in effect call for glyph-areas to be substituted, inserted, or deleted, then the substituted or inserted glyph-areas appear in the area tree in the corresponding place, and the deleted glyph-areas do not appear in the area tree. Deletions occur when a glyph-area which is last within a subset Si, has a suppress-at-line-break value of suppress, provided that i < n and Bi+1 is a line-area. Deletions also occur when a glyph-area which is first within a subset Si, has a suppress-at-line-break value of suppress, provided that i > 1 and Bi-1 is a line-area. Insertions and substitutions may occur because of addition of hyphens or spelling changes due to hyphenation, or glyph image construction from syllabification, or ligature formation.

Substitutions that replace a sequence of glyph-areas with a single glyph-area should only occur when the margin, border, and padding in the inline-progression-direction (start- and end-), baseline-shift, and letter-spacing values are zero, treat-as-word-space is false, and the values of all other relevant traits match (i.e., alignment-adjust, alignment-baseline, color trait, background traits, dominant-baseline-identifier, font traits, text-depth, text-altitude, glyph-orientation-horizontal, glyph-orientation-vertical, line-height, line-height-shift-adjustment, text-decoration, text-shadow).

NOTE: 

Line-areas do not receive the background traits or text-decoration of their generating formatting object, or any other trait that requires generation of a mark during rendering.

Inline-building[top]

This section describes the ordering constraints that apply to formatting an fo:inline or similar inline-level object.

An inline-level formatting object F which constructs one or more inline-areas does so by placing normal inline-areas and/or anchor inline-areas returned to F by its child formatting objects as children of inline-areas which it generates.

For each such formatting object F, it must be possible to form an ordered partition P consisting of ordered subsets S1, S2, ..., Sn of the normal and/or anchor inline-areas returned by the child formatting objects, such that the following are all satisfied:

1. Each subset consists of a sequence of inline-areas, or of a single block-area.

2. The ordering of the partition follows the ordering of the formatting object tree, as defined above.

3. The partitioning occurs at legal line-breaks, as defined above.

4. Forced line-breaks are respected, as defined above.

5. The partition follows the ordering of the area tree, except for certain glyph substitutions and deletions, as defined above.