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Please note that this page was not updated after the clarification about space traits by the XSL FO SG!!!
Example 0
This is the one from the spec (in chapter 4.3.1).
<fo:block space-before="10pt">
<fo:block space-before="4pt" space-before.conditionality="retain">
<fo:block space-before="5pt">
<fo:block>before break</fo:block>
<fo:block>after break</fo:block>
</fo:block>
</fo:block>
</fo:block>For both cases, break before the above sequence and between "before break" and "after break":
The 10pt space is suppressed due to rule 1. It is conditional and begins a reference area.
The rest of the spaces are non-forcing, so rule 2 is skipped.
The 4pt space is suppressed under rule 3. It has the same precedence as the 5pt space but has a smaller optimum length. Since there will only be one resolved space it will be 5pt.
Example 1
A simple (conditional) space.
<fo:block>first line</fo:block> <fo:block space-before="10pt"> <fo:block>before break</fo:block> <fo:block>after break</fo:block> </fo:block>
The break after "first line" does not produce a 10pt space because the space is conditional.
The break after "break before" does not produce a 10pt space because the space is conditional.
Element list:
box w=lh for "first line" penalty w=0 p=0 for the break possibility after "first line" aux glue w=10pt for the space in case there is no break box w=lh for "before break" penalty w=0 p=0 for the break possibility after "before break" box w=lh for "after break"
Example 2
A non-conditional space.
<fo:block>first line</fo:block> <fo:block space-before="10pt" space-before.conditionality="retain"> <fo:block>before break</fo:block> <fo:block>after break</fo:block> </fo:block>
The break after "first line" produces a 10pt space because the space is retained.
The break after "break before" produces a 10pt space because the space is retained.
Element list:
box w=lh for first block penalty w=0 p=0 for the break possibility box w=0 penalty p=INF aux glue w=10pt for space-before box w=lh for "before break" penalty w=0 p=0 for the break possibility after "before break" aux glue w=-10pt for compensating the space glue below in the no-break condition box w=0 penalty p=INF aux glue w=10pt for space-before box w=lh for "after break"
Example 3
The collapsing of the adjacent conditional spaces according to rule 3.
<fo:block space-after="10pt">first block</fo:block> <fo:block space-before="10pt">second block</fo:block>
Break between the blocks:
We have two S' which each contains one space specifier.
S'[1]: The space-after on the first block is suppressed under rule 1 in 4.3.1.
S'[2]: The space-before on the second block is suppressed under rule 1 in 4.3.1.
No break between the blocks:
S' consists of both space-specifiers in this example (Case 3a under 4.2.5. Stacking Constraints).
Rule 1 does not apply. No forcing space-specifiers (rule 2). Both non-forcing space-specifiers collapse to a single space with 10pt.
Element list:
box w=lh for first block penalty w=0 p=0 for the break possibility glue w=10pt y=0 z=0 box w=lh for second block
Example 4
<fo:block space-after="10pt" space-after.conditionality="retain">first block</fo:block> <fo:block space-before="10pt">second block</fo:block>
Break between the blocks:
The first space specifier is retained. The second is conditional and is suppressed.
Element list:
box w=lh for first block glue w=10pt y=0 z=0 penalty w=0 p=0 for the break possibility box w=lh for second block
Example 5
<fo:block space-after="10pt" space-after.conditionality="retain">first block</fo:block> <fo:block space-before="10pt" space-before.conditionality="retain">second block</fo:block>
Break between the blocks:
Both space specifiers are retained.
That means that with a break we have more space than without a break, and we need a negative glue (glue #2) to compensate this.
Element list:
(the full case: glue #1 - penalty - glue #2 - box - PENALTY - glue #3):
box w=lh for first block glue w=10pt y=0 z=0 penalty w=0 p=0 for the break possibility glue w=-10pt y=0 z=0 box w=0 penalty w=0 p=INF glue w=10pt y=0 z=0 box w=lh for second block
Example 6 and 7 removed due to mistakes.
Example 8
Bringing border and padding into play.
<fo:block space-before="10pt" padding-before="5pt" border-before-style="solid" border-before-width="2pt"> first line <fo:block space-before="6pt">second line</fo:block> </fo:block>
We look at the break possibility between the first and the second line here. All spaces, paddings and borders are conditional. Since the block area for "second line" begins a reference-area here, according to 4.3.1, the widths for border and padding from the parent block both collapse to zero, so S' consists of both space-specifiers in this example. Both space-specifiers are conditional and are therefore suppressed under rule 1, as they have a stacking constraint when border and padding collapse to zero.
Only in the non-break condition will the second space-before be generated.
Element list:
box w=lh for first line penalty w=0 p=0 for the break possibility aux glue w=6pt y=0 z=0 box w=lh for second line
Example 9
Bringing border and padding into play (continued).
<fo:block space-before="10pt" padding-before="5pt" border-before-style="solid" border-before-width="2pt" border-before-width.conditionality="retain"> first line <fo:block space-before="6pt">second line</fo:block> </fo:block>
Again we look at the break possibilty between the first and second line as in the previous example. All spaces and paddings are conditional. Only the border is non-conditional (the only change to the previous example). In the break case, we begin a reference-area here, but the border interrupts the suppressing of space elements (there's no stacking constraint anymore). So only the first space-before is suppressed. After that the border is added. The following padding is suppressed, but not the space after that (it does not begin a reference area because of the retained outer border).
In the no-break case, there is simply a 6pt space-before before "second line".
Element list:
box w=0 penalty p=INF glue w=17pt (10pt space-before + 2pt border + 5pt padding) box w=lh for "first line" penalty w=0 p=0 for the break possibility glue w=-2pt (8pt - 2pt = 6pt for the space-before in the no-break case) box w=0 penalty p=INF glue w=8pt (2pt border + 6pt space-before) box w=lh for "second line"