Table of contents

Appendices

7.13 Area Alignment Properties

The area alignment properties control the alignment of child areas with respect to their parent areas. The parent area is given a frame of reference through its scaled-baseline-table. A scaled-baseline-table is a compound value with three components: a baseline-identifier for the dominant-baseline, a derived baseline-table with positions for the baselines expressed in design space coordinates, and a baseline-table font-size that is used to scale the positions of the baselines in that baseline table. In a scaled-baseline-table, the positions of the baselines can be adjusted by multiplying the design-space coordinate values by the baseline-table font-size.

The positions of these baselines are illustrated in the following figure:

This figure shows samples of Gurmukhi (a hanging Indic script), Latin and ideographic scripts together with most of the baselines defined below. The thin line around the ideographic glyphs symbolizes the em box in which these glyphs are centered. In this figure, the position of the "text-before-edge" and "text-after-edge" baselines is computed assuming that the "alphabetic" baseline is the dominant-baseline. The "central" baseline has been omitted from the figure, but it lies halfway between the "text-before-edge" and "text-after-edge" baselines, just about where the "math" baseline is shown.

The baseline-identifiers below are used in this specification. Some of these are determined by baseline-tables contained in a font as described in [font-model] . Others are computed from other font characteristics as described below. Whether determined by the font or computed, a derived baseline-table is constructed with positions for each of the baselines below.

alphabetic

This identifies the baseline used by most alphabetic and syllabic scripts. These include, but are not limited to, many Western, Southern Indic, Southeast Asian (non-ideographic) scripts.

ideographic

This identifies the baseline used by ideographic scripts. For historical reasons, this baseline is at the bottom of the ideographic em box and not in the center of the ideographic em box. See the "central" baseline. The ideographic scripts include Chinese, Japanese, Korean, and Vietnamese Chu Nom.

hanging

This identifies the baseline used by certain Indic scripts. These scripts include Devanagari, Gurmukhi and Bengali.

mathematical

This identifies the baseline used by mathematical symbols.

central

This identifies a computed baseline that is at the center of the em box. This baseline lies halfway between the text-before-edge and text-after-edge baselines.

NOTE: 

For ideographic fonts, this baseline is often used to align the glyphs; it is an alternative to the ideographic baseline.

middle

This identifies a baseline that is offset from the alphabetic baseline in the shift-direction by 1/2 the value of the x-height font characteristic. The position of this baseline may be obtained from the font data or, for fonts that have a font characteristic for "x-height", it may be computed using 1/2 the "x-height". Lacking either of these pieces of information, the position of this baseline may be approximated by the "central" baseline.

text-before-edge

This identifies the before-edge of the em box. The position of this baseline may be specified in the baseline-table or it may be calculated.

NOTE: 

The position of this baseline is normally around or at the top of the ascenders, but it may not encompass all accents that can appear above a glyph. For these fonts the value of the "ascent" font characteristic is used. For ideographic fonts, the position of this baseline is normally 1 em in the shift-direction from the "ideographic" baseline. However, some ideographic fonts have a reduced width in the inline-progression-direction to allow tighter setting. When such a font, designed only for vertical writing-modes, is used in a horizontal writing-mode, the "text-before-edge" baseline may be less than 1 em from the text-after-edge.

text-after-edge

This identifies the after-edge of the em box. The position of this baseline may be specified in the baseline-table or it may be calculated.

NOTE: 

For fonts with descenders, the position of this baseline is normally around or at the bottom of the descenders. For these fonts the value of the "descent" font characteristic is used. For ideographic fonts, the position of this baseline is normally at the "ideographic" baseline.

There are, in addition, two computed baselines that are only defined for line areas. For each line-area, there is a dominant-baseline, a baseline-table and a baseline-table font-size which are those of the nearest ancestor formatting object that completely contains the whole line. The "before-edge" and "after-edge" baselines are defined as follows.

before-edge

The offset of the "before-edge" baseline of the line from the dominant-baseline of the line is determined by ignoring all inline-areas whose alignment-baseline is either "before-edge" or "after-edge". For the "before-edge", extents are measured from the dominant-baseline in the direction toward the top of the reference-area. The top of the reference-area is defined by the reference-area's reference-orientation. The "before-edge" baseline offset is set to the maximum extent of the "before-edges" of the allocation-rectangles of the remaining areas. If all the inline-areas in a line-area are aligned either to the "before-edge" or to the "after-edge", then use the offset of the "text-before-edge" baseline of the line as the offset of the "before-edge" baseline of the line.

after-edge

The offset of the "after-edge" baseline of the line from the dominant-baseline of the line is determined by ignoring all inline-areas whose alignment-baseline is after-edge. For the "after-edge", extents are measured from the dominant-baseline in the direction toward the bottom of the reference-area. The top of the reference-area is defined by the reference-area's reference-orientation. The "after-edge" baseline offset is set to the negative of the maximum of (1) the maximum extent of the "after-edges" of the allocation-rectangles of the remaining areas and (2) the maximum height of the allocation-rectangles of the areas that are ignored minus the offset of the "before-edge" baseline of the line.

NOTE: 

If all the inline-areas in a line-area are aligned to the "after-edge" then the specification for the "before-edge" will set the "before-edge" baseline to coincide with the "text-before-baseline" of the line. Then, case (2) above will determine the offset to the "after-edge" baseline. In this case the allocation-rectangle of one of the areas will extend from the "before-edge" baseline to the "after-edge" baseline.

NOTE: 

The above specifications for "before-edge" and "after-edge" have the following three properties: (1) the allocation-rectangles of all the areas are below the "before-edge", (2) the allocation-rectangles of all the areas are above the "after-edge", and (3) the distance between the "before-edge" and the "after-edge" cannot be decreased without violating (1) or (2). The specified placement of the "before-edge" and "after-edge" is not the only way that (1)-(3) can be satisfied, but it is the only way they can be satisfied with the smallest possible offset to the "before-edge".

Examples showing "before-edge" and "after-edge" alignment:

The rectangles with lines or arrows are images with an intrinsic size as shown. The rectangles with no arrows represent images that receive the default, dominant baseline, alignment. The alignment of the other rectangles is at the furthest point from the arrow head (which is in the middle when there are two arrowheads). Examples 1 and 2 show the "before-edge" alignment is determined by the tallest non-"before-edge" aligned objects: in example 1 this is the default aligned, arrowhead free rectangular image and in example 2 this is the double headed arrow rectangle. Examples 3 and 4 show defaulting to the "text-before-edge" when all the areas have either "before-edge" or "after-edge" alignment. In example 3, the images with "before-edge" alignment has a taller member than do the "after-edge" aligned images. In example 4, the tallest image is in the "after-edge" aligned set. Example 5 is a repetition of example 2 with largest image being an "after-edge" aligned image.

There are also four baselines that are defined only for horizontal writing-modes.

top

This baseline is the same as the "before-edge" baseline in a horizontal writing-mode and is undefined in a vertical writing mode.

text-top

This baseline is the same as the "text-before-edge" baseline in a horizontal writing-mode and is undefined in a vertical writing mode.

bottom

This baseline is the same as the "after-edge" baseline in a horizontal writing-mode and is undefined in a vertical writing mode.

text-bottom

This baseline is the same as the "text-after-edge" baseline in a horizontal writing-mode and is undefined in a vertical writing mode.

The alignment of a formatting object with respect to its parent is determined by three things: the scaled-baseline-table of the parent and the alignment-baseline and alignment-point of the formatting object being aligned. Prior to alignment, the scaled-baseline-table of the parent may be shifted. The property specifications below provide the information necessary to align the parent and child formatting objects.

There are four properties that control alignment of formatting objects to the above set of baselines. These properties are all independent and are designed so that typically only the specification of one of the properties is needed to achieve a particular alignment goal.

The primary baseline alignment property is the "dominant-baseline" property. This property has a compound value with three components. The dominant-baseline-identifier component is the default alignment-baseline to be used when aligning two inline-areas. The baseline-table component specifies the positions of the baselines in the font design space coordinates. (See [font-model] .) The baseline-table acts something like a musical staff; it defines particular points along the block-progression-direction to which glyphs and inline formatting objects can be aligned. The baseline-table font-size component provides a scaling factor for the baseline-table.

For convenience, the specification will sometimes refer to the baseline identified by the dominant-baseline-identifier component of the "dominant-baseline" property as the "dominant baseline" (in an abuse of terminology).

A simple example of alignment is shown in the following figure. The figure shows the presentation of two inline formatting objects, one inside the other. These inline formatting objects make up the content of a line in a block where the writing-mode is "lr-tb" and the font is "Helvetica". The structure of the example is as follows:

<fo:inline>Apex <fo:inline>Top</fo:inline></fo:inline>

Because no properties are specified, the initial values apply. Since a horizontal writing-mode is in use, the dominant-baseline-identifier is set to "alphabetic" and the baseline-table is taken from the nominal-font for the block in which the line appears, which, in this case, is Helvetica.

In the figure, the positions of the baselines relative to the current font size are shown as red (staff) lines. These lines are labeled with abbreviations of the names of the baselines (e.g., TBE for "text-before-edge"). The baseline identified by the dominant-baseline-identifier (A) is shown in blue. There is a break in the staff lines to separately show the inner inline formatting object. This is not necessary for this example, but this distinction will become important in subsequent examples.

The "alignment-baseline" property is the primary control on the positioning of an inner formatting object with respect to its parent. For all but fo:character, the initial value of the "alignment-baseline" property is "baseline". This aligns the dominant-baseline of the inner inline formatting object with the dominant baseline of the outer inline formatting object. This is shown by the short blue line that connects the two separated staffs (A) in the figure.

The glyphs determined by the fo:characters that are in the content of the two formatting objects are aligned based on the script to which the glyph belongs. Since this example only has Latin glyphs, they are aligned to the "alphabetic" baseline.

An inner inline formatting object containing Latin characters aligned to an outer inline formatting object also containing Latin characters.

In the next figure, the content of the inner inline formatting object is in Gurmukhi, the script of the Punjabi language. The Gurmukhi syllables are read as, "guru". Rather than use Unicode values for these characters, they are symbolized by placing the Latin transliteration in italic type. The structure of the example becomes:

<fo:inline>Apex <fo:inline>guru</fo:inline></fo:inline>

The only change from the previous example is that the glyphs of the Gurmukhi script are aligned to the "hanging" baseline of the inner inline formatting object. The alignment of that formatting object itself, with respect to the outer inline formatting object, is unchanged.

An inner inline formatting object containing Gurmukhi characters aligned to an outer inline formatting object containing Latin characters.

In the next figure, fragments of the text of the previous examples make up the content of the outer inline formatting object. The inner inline formatting object has a change of font-size, however. The structure is:

<fo:inline>Apguru
  <fo:inline font-size='.75em'>
    Exji
  </fo:inline>
</fo:inline>

In this example, the alignment of the inner inline formatting object itself does not change, nor does the alignment of the smaller glyphs inside the inner formatting object. The Latin glyphs are still aligned to the "alphabetic" baseline and the Gurmukhi glyphs, which are pronounced "ji" are aligned to the "hanging" baseline. Note also that just changing the "font-size" property did not change the baseline-table in effect in the inner inline formatting object.

The inner inline formatting object has a reduced font-size.

The next figure is equivalent to the previous example with the Gurmukhi character replaced by ideographic characters. These are aligned to the "ideographic" baseline.

The previous figure re-done with ideographic glyphs instead of Gurmukhi glyphs. The em boxes are shown for the ideograms to clarify the alignment of these glyphs.

To change the scaling of the lines of the baseline table, it is necessary to use the "dominant-baseline" property on the inner inline formatting object. The value of "reset-size" causes the baseline-table font-size to be reset from the font-size of the formatting object on which the "dominant-baseline" property appears. The next figure shows the effect of this, using the structure:

<fo:inline>Apguru
  <fo:inline font-size='.75em'
             dominant-baseline='reset-size'>
     Exji
  </fo:inline>
</fo:inline>

The alignment of the inner inline formatting object, with respect to the outer inline formatting object, is still determined by aligning the dominant baselines. But, the baseline-table of the inner inline formatting object has been rescaled to the font-size of the inner inline formatting object. Hence the smaller glyphs align with each other.

The baseline-table of the inner inline formatting object has been re-sized to match the font-size of the inner inline formatting object.

But, what if it is more important that the small Gurmukhi glyphs align with the large Gurmukhi glyphs than having the Latin glyphs align. There are at least two ways to achieve this. The structure:

<fo:inline dominant-baseline='hanging'>Apguru
  <fo:inline font-size='.75em'
             dominant-baseline='reset-size'>
     Exji
  </fo:inline>
</fo:inline>

is illustrated in the next figure. The "hanging" baseline becomes the dominant baseline and the initial value of the "alignment-baseline" property causes the (newly) dominant "hanging" baselines to be aligned as is shown by the connection of the blue baselines.

Changing the dominant baseline to the "hanging" baseline causes the inner inline formatting object to be aligned on its parent's "hanging" baseline.

It is also possible to achieve the effect of the above figure without changing the dominant baseline. Instead it is sufficient to explicitly specify that the inner inline formatting object is aligned on its "hanging" baseline. This is done by:

<fo:inline>Apguru
  <fo:inline font-size='.75em'
             dominant-baseline='reset-size'
             alignment-baseline='hanging'>
     Exji
  </fo:inline>
</fo:inline>

The only change this approach would make in the above figure is to color the "hanging" baseline red and keep the "alphabetic" baseline as the (blue) dominant baseline. This baseline in the inner inline formatting object would not (as it does not in the above figure) align with the "alphabetic" baseline in the outer inline formatting object.

The third baseline alignment property is the "baseline-shift" property. Like the properties other than the "dominant-baseline" property, this property does not change the baseline-table or the baseline-table font-size. It does shift the whole baseline table of the parent formatting object so that when an inner inline formatting object is aligned to one of the parents baselines, the position of the inner inline formatting object is shifted. This is illustrated in the next figure. The structure which creates this figure is:

<fo:inline>Ap
  <fo:inline baseline-shift='super'>1ji</fo:inline>
</fo:inline>

Because the whole set of baseline-table staff lines are shifted to the position of the superscript baseline: it does not matter to which baseline the glyphs in the superscript are aligned. The European number "1" is aligned to the "alphabetic" baseline and the Gurmukhi syllable "ji" is aligned to the "hanging" baseline.

Using a "baseline-shift" for a superscript (or a subscript).

It is more common for the font-size of the superscript text to be smaller than the font-size of the text to which it is appended. Consider:

<fo:inline>Ap
  <fo:inline font-size='.75em'
             baseline-shift='super'>
    1ji
  </fo:inline>
</fo:inline>

Because changing the font-size on a superscript (or subscript) is common, this is the one case where changing the font-size does cause the baseline-table font-size to be reset when the "dominant-baseline" property has its initial value. After the rescaling, the default alignment to the dominant baseline positions the inline formatting object for the superscript to the dominant baseline position in the shifted baseline-table of the parent formatting object.

Reducing the font-size of the superscript automatically resets the baseline-table size so that mixed languages in the superscript stay mutually aligned.

The fourth alignment property is the "alignment-adjust" property. This property is primarily used for objects, such as some graphics, that do not belong to a particular script and do not have a predefined alignment point. The "alignment-adjust" property allows the author to assign where, on the start-edge of the object, the alignment point for that object lies.

alignment-adjust[top]

XSL Definition:

The "alignment-adjust" property allows more precise alignment of areas generated by formatting objects, in particular for formatting objects, such as graphics, that do not have a baseline-table or lack the desired baseline in their baseline-table. With the "alignment-adjust" property, the position of the baseline identified by the "alignment-baseline" can be explicitly determined.

Values for the property have the following meaning:

auto

For a glyph, the alignment-point is the intersection of the start-edge of the allocation-rectangle of the glyph-area and the block-progression-direction position of the alignment-point from the font as specified in [font-model] . For other inline-areas, the alignment-point is at the intersection of the start-edge of the allocation-rectangle and the baseline identified by the "alignment-baseline" property if this baseline exists in the baseline-table for the dominant-baseline for the inline-area. If the baseline-identifier does not exist in the baseline-table for the glyph or other inline-area, then the User Agent may either use heuristics to determine where that missing baseline would be or may use the dominant-baseline as a fallback. For areas generated by a fo:external-graphic, or fo:instream-foreign-object, the alignment point is at the intersection of the start-edge and after-edge of the allocation-rectangle of the area.

baseline

The alignment-point is at the intersection of the start-edge of the allocation-rectangle and the dominant-baseline of the area.

before-edge

The alignment-point is at the intersection of the start-edge of the allocation-rectangle and the "before-edge" baseline of the area.

text-before-edge

The alignment-point is at the intersection of the start-edge of the allocation-rectangle and the "text-before-edge" baseline of the area.

central

The alignment-point is at the intersection of the start-edge of the allocation-rectangle and the "central" baseline of the area.

middle

The alignment-point is at the intersection of the start-edge of the allocation-rectangle and the "middle" baseline of the area.

after-edge

The alignment-point is at the intersection of the start-edge of the allocation-rectangle and the "after-edge" baseline of the area.

text-after-edge

The alignment-point is at the intersection of the start-edge of the allocation-rectangle and the "text-after-edge" baseline of the area.

ideographic

The alignment-point is at the intersection of the start-edge of the allocation-rectangle and the "ideographic" baseline of the area.

alphabetic

The alignment-point is at the intersection of the start-edge of the allocation-rectangle and the "alphabetic" baseline of the area.

hanging

The alignment-point is at the intersection of the start-edge of the allocation-rectangle and the "hanging" baseline of the area.

mathematical

The alignment-point is at the intersection of the start-edge of the allocation-rectangle and the "mathematical" baseline of the area.

top

The alignment-point is at the intersection of the start-edge of the allocation-rectangle and the "top" baseline of the area if the writing-mode is horizontal. Otherwise, the dominant-baseline is used.

bottom

The alignment-point is at the intersection of the start-edge of the allocation-rectangle and the "bottom" baseline of the area if the writing-mode is horizontal. Otherwise, the dominant-baseline is used.

text-top

The alignment-point is at the intersection of the start-edge of the allocation-rectangle and the "text-top" baseline of the area if the writing-mode is horizontal. Otherwise, the dominant-baseline is used.

text-bottom

The alignment-point is at the intersection of the start-edge of the allocation-rectangle and the "text-bottom" baseline of the area if the writing-mode is horizontal. Otherwise, the dominant-baseline is used.

<percentage>

The computed value of the property is this percentage multiplied by the area's computed "height" if the area is generated by an fo:external-graphic or fo:instream-foreign-object, the "font-size" if the area was generated by an fo:character, and the "line-height" otherwise. The alignment-point is on the start-edge of the allocation-rectangle of the area being aligned. Its position along the start-edge relative to the intersection of the dominant-baseline and the start-edge is offset by the computed value. The offset is opposite to the shift-direction if that value is positive and in the shift-direction if that value is negative value). A value of "0%" makes the dominant-baseline the alignment point.

<length>

The alignment-point is on the start-edge of the allocation-rectangle of the area being aligned. Its position along the start-edge relative to the intersection of the dominant-baseline and the start-edge is offset by <length> value. The offset is opposite to the shift-direction if that value is positive and in the shift-direction if that value is negative. A value of "0cm" makes the dominant-baseline the alignment point.

Implementations must support at least one of the "alignment-adjust" values defined in this Recommendation.

alignment-baseline[top]

XSL Definition:

This property specifies how an object is aligned with respect to its parent. That is, to which of the parent's baselines the alignment-point of this object is aligned. The alignment-adjust property specifies how the alignment point is determined. It defaults to the baseline with the same name as the computed value of the alignment-baseline property. That is, the position of "ideographic" alignment-point in the block-progression-direction is the position of the "ideographic" baseline in the baseline-table of the object being aligned.

Values have the following meanings:

auto

The computed value depends on the kind of object on which it is being used. For fo:character, the value is the dominant-baseline of the script to which the character belongs. If the value of the "script" property on the parent formatting object is other than "auto" then use the baseline for that script; otherwise, use the dominant-baseline of the parent. For all other objects, the value is computed as for the "baseline" value.

baseline

The alignment-point of the object being aligned is aligned with the dominant-baseline of the parent area.

before-edge

The alignment-point of the object being aligned is aligned with the "before-edge" baseline of the parent area.

text-before-edge

The alignment-point of the object being aligned is aligned with the "text-before-edge" baseline of the parent area.

central

The alignment-point of the object being aligned is aligned with the "central" baseline of the parent area.

middle

The alignment-point of the object being aligned is aligned with the "middle" baseline of the parent area.

after-edge

The alignment-point of the object being aligned is aligned with the "after-edge" baseline of the parent area.

text-after-edge

The alignment-point of the object being aligned is aligned with the "text-after-edge" baseline of the parent area.

ideographic

The alignment-point of the object being aligned is aligned with the "ideographic" baseline of the parent area.

alphabetic

The alignment-point of the object being aligned is aligned with the "alphabetic" baseline of the parent area.

hanging

The alignment-point of the object being aligned is aligned with the "hanging" baseline of the parent area.

mathematical

The alignment-point of the object being aligned is aligned with the "mathematical" baseline of the parent area.

top

The alignment-point of the object being aligned is aligned with the "top" baseline of the parent area if the writing-mode is horizontal. Otherwise, the dominant-baseline is used.

bottom

The alignment-point of the object being aligned is aligned with the "bottom" baseline of the parent area if the writing-mode is horizontal. Otherwise, the dominant-baseline is used.

text-top

The alignment-point of the object being aligned is aligned with the "text-top" baseline of the parent area if the writing-mode is horizontal. Otherwise, the dominant-baseline is used.

text-bottom

The alignment-point of the object being aligned is aligned with the "text-bottom" baseline of the parent area if the writing-mode is horizontal. Otherwise, the dominant-baseline is used.

Implementations must support at least one of the "alignment-baseline" values defined in this Recommendation.

baseline-shift[top]

XSL Definition:

The "baseline-shift" property allows repositioning of the dominant-baseline relative to the dominant-baseline of the parent area. The shifted object might be a subscript or superscript. Within the shifted object, the whole baseline-table is offset; not just a single baseline. The amount of the shift is determined from information from the parent area, the subscript or superscript offset from the nominal-font of the parent area, percent of the "line-height" of the parent area or an absolute value.

When the value of "baseline-shift" is other than "0", then the baseline-table font-size component of the "dominant-baseline" property is re-computed to use the "font-size" applicable to the formatting object on which the non-zero "baseline-shift" property is specified.

Values for the property have the following meaning:

baseline

There is no baseline shift; the dominant-baseline remains in its original position.

sub

The dominant-baseline is shifted to the default position for subscripts. The offset to this position is determined using the font data for the nominal font. Because in most fonts the subscript position is normally given relative to the "alphabetic" baseline, the User Agent may compute the effective position for subscripts for superscripts when some other baseline is dominant. The suggested computation is to subtract the difference between the position of the dominant baseline and the position of the "alphabetic" baseline from the position of the subscript. The resulting offset is determined by multiplying the effective subscript position by the dominant baseline-table font-size. If there is no applicable font data the User Agent may use heuristics to determine the offset.

super

The dominant-baseline is shifted to the default position for superscripts. The offset to this position is determined using the font data for the nominal font. Because in most fonts the superscript position is normally given relative to the "alphabetic" baseline, the User Agent may compute the effective position for superscripts when some other baseline is dominant. The suggested computation is to subtract the difference between the position of the dominant baseline and the position of the "alphabetic" baseline from the position of the superscript. The resulting offset is determined by multiplying the effective superscript position by the dominant baseline-table font-size. If there is no applicable font data the User Agent may use heuristics to determine the offset.

<percentage>

The computed value of the property is this percentage multiplied by the computed "line-height" of the parent area. The dominant-baseline is shifted in the shift-direction (positive value) or opposite to the shift-direction (negative value) of the parent area by the computed value. A value of "0%" is equivalent to "baseline".

<length>

The dominant-baseline is shifted in the shift-direction (positive value) or opposite to the shift-direction (negative value) of the parent area by the <length> value. A value of "0cm" is equivalent to "baseline".

NOTE: 

Although it may seem that "baseline-shift" and "alignment-adjust" properties are doing the same thing, there is an important although, perhaps, subtle difference. For "alignment-adjust" the percentage values refer to the "line-height" of the area being aligned. For "baseline-shift" the percentage values refer to the "line-height" of the parent. Similarly, it is the "sub" and "super" offsets of the parent that are used to align the shifted baseline rather than the "sub" or "super" offsets of the areas being positioned. To ensure a consistent subscript or superscript position, it makes more sense to use the parent as the reference rather than the subscript formatting object which may have a changed "line-height" due to "font-size" changes in the subscript or superscript formatting object.

Using the "alignment-adjust" property is more suitable for positioning objects, such as graphics, that have no internal textual structure. Using the "baseline-shift" property is intended for subscripts and superscripts where the positioned object may itself be a textual object. The baseline-shift provides a way to define a specific baseline offset other than the named offsets that are defined relative to the dominant-baseline. In addition, having "baseline-shift" makes it easier for tool to generate the relevant properties; many formatting programs already have a notion of baseline shift.

display-align[top]

XSL Definition:

This property specifies the alignment, in the block-progression-direction, of the areas that are the children of a reference-area.

Values for the property have the following meaning:

auto

If the "relative-align" property applies to this formatting object the "relative-align" property is used. If not, this value is treated as if "before" had been specified.

before

The before-edge of the allocation-rectangle of the first child area is placed coincident with the before-edge of the content-rectangle of the reference-area.

center

The child areas are placed such that the distance between the before-edge of the allocation-rectangle of the first child area and the before-edge of the content-rectangle of the reference-area is the same as the distance between the after-edge of the allocation-rectangle of the last child area and the after-edge of the content-rectangle of the reference-area.

after

The after-edge of the allocation-rectangle of the last child area is placed coincident with the after-edge of the content-rectangle of the reference-area.

dominant-baseline[top]

XSL Definition:

The "dominant-baseline" property is used to determine or re-determine a scaled-baseline-table. A scaled-baseline-table is a compound value with three components: a baseline-identifier for the dominant-baseline, a derived baseline-table and a baseline-table font-size. Some values of the property re-determine all three values; other only re-establish the baseline-table font-size. When the initial value, "auto", would give an undesired result, this property can be used to explicitly set the desired scaled-baseline-table.

NOTE: 

The derived baseline-table is constructed using a baseline-table in the font that corresponds to the computed value of the "writing-mode".

Values for the property have the following meaning:

auto

If this property occurs on a block-level formatting object, then the computed value depends on the value of the "script" property. There are two cases. If the value of the "script" property is "auto", then, if the "writing-mode" is horizontal, then the baseline-identifier for the dominant baseline is set to be "alphabetic", else if the "writing-mode" is vertical, then the baseline-identifier for the dominant baseline is set to be "central". On the other hand, if the value of the "script" property is anything other than "auto", then the value of the "script" property is used to select the baseline-identifier for the dominant baseline. The mapping from script to baseline-identifier is taken from the nominal font. The derived baseline-table is constructed using the baseline-table in the nominal font that corresponds to the baseline-identifier for the dominant baseline. The baseline-table font-size is changed to the value of the "font-size" property on this formatting object.

Otherwise, if this property is not on a block-level formatting object, then the baseline-identifier for the dominant baseline, the derived baseline-table, and baseline-table font-size remain the same as those of the parent formatting object. If the computed "baseline-shift" value actually shifts the baseline, then the baseline-table font-size is set to the value of the "font-size" property on the formatting object on which the "dominant-baseline" property occurs, otherwise the baseline-table font-size remains the same as that of the parent formatting object. If there is no parent formatting object, the derived baseline-table is constructed as above for block-level formatting-objects.

use-script

The "script" property is used to select the baseline-identifier for the dominant baseline. The mapping from script to baseline-identifier is taken from the nominal font. The derived baseline-table is constructed using the baseline-table in the nominal font that corresponds to the baseline-identifier for the dominant baseline. The baseline-table font-size is changed to the value of the "font-size" property on this formatting object.

no-change

The dominant-baseline, the baseline-table, and the baseline-table font-size remain the same as that of the parent formatting object.

reset-size

The dominant-baseline and the baseline-table remain the same, but the baseline-table font-size is changed to the value of the "font-size" property on this formatting object. This re-scales the baseline-table for the current "font-size".

ideographic

The baseline-identifier for the dominant-baseline is set to be "ideographic". The derived baseline-table is constructed using the "ideographic" baseline-table in the nominal font. The baseline-table font-size is changed to the value of the "font-size" property on this formatting object.

alphabetic

The baseline-identifier for the dominant-baseline is set to be "alphabetic". The derived baseline-table is constructed using the "alphabetic" baseline-table in the nominal font. The baseline-table font-size is changed to the value of the "font-size" property on this formatting object.

hanging

The baseline-identifier for the dominant-baseline is set to be "hanging". The derived baseline-table is constructed using the "hanging" baseline-table in the nominal font. The baseline-table font-size is changed to the value of the "font-size" property on this formatting object.

mathematical

The baseline-identifier for the dominant-baseline is set to be "mathematical". The derived baseline-table is constructed using the "mathematical" baseline-table in the nominal font. The baseline-table font-size is changed to the value of the "font-size" property on this formatting object.

central

The baseline-identifier for the dominant-baseline is set to be "central". The derived baseline-table is constructed from the defined baselines in a baseline-table in the nominal font. That font baseline-table is chosen using the following priority order of baseline-table names: "ideographic", "alphabetic", "hanging", "mathematical". The baseline-table font-size is changed to the value of the "font-size" property on this formatting object.

middle

The baseline-identifier for the dominant-baseline is set to be "middle". The derived baseline-table is constructed from the defined baselines in a baseline-table in the nominal font. That font baseline-table is chosen using the following priority order of baseline-table names: "alphabetic", "ideographic", "hanging", "mathematical". The baseline-table font-size is changed to the value of the "font-size" property on this formatting object.

text-after-edge

The baseline-identifier for the dominant-baseline is set to be "text-after-edge". The derived baseline-table is constructed from the defined baselines in a baseline-table in the nominal font. The choice of which font baseline-table to use from the baseline-tables in the nominal font is implementation defined. The baseline-table font-size is changed to the value of the "font-size" property on this formatting object.

NOTE: 

Using the following priority order of baseline-table names: "alphabetic", "ideographic", "hanging", "mathematical" is probably a reasonable strategy for determining which font baseline-table to use.

text-before-edge

The baseline-identifier for the dominant-baseline is set to be "text-before-edge". The derived baseline-table is constructed from the defined baselines in a baseline-table in the nominal font. The choice of which baseline-table to use from the baseline-tables in the nominal font is implementation defined. The baseline-table font-size is changed to the value of the "font-size" property on this formatting object.

NOTE: 

Using the following priority order of baseline-table names: 'alphabetic', 'ideographic', 'hanging', 'mathematical' is probably a reasonable strategy for determining which font baseline-table to use.

If there is no baseline-table in the nominal font or if the baseline-table lacks an entry for the desired baseline, then the User Agent may use heuristics to determine the position of the desired baseline.

Implementations must support at least one of the "dominant-baseline" values defined in this Recommendation.

relative-align[top]

XSL Definition:

This property specifies the alignment, in the block-progression-direction, between two or more areas. If the "display-align" property applies to this formatting object and has a value other than "auto" this property is ignored.

Values for the property have the following meaning:

before

For an fo:table-cell: for each row, the first child area of all the cells that start in the row and that have this value is placed such that the before-edge of the content-rectangle is placed at the same distance from the row grid. In addition, at least, one of these first child areas of the cells has to be placed with the before-edge of its allocation-rectangle coincident with the before-edge of the content-rectangle of the table-cell.

For an fo:list-item the before-edge of the first area descendant generated by the fo:list-item-label is placed coincident with the before-edge of the area generated by the fo:list-item. Similarly the before-edge of the first area descendant generated by the fo:list-item-body is placed coincident with the before-edge of the area generated by the fo:list-item.

baseline

For an fo:table-cell: for each row, the first child area of all the cells that start in the row and that have this value is placed such that the dominant-baseline, as specified on the fo:table-row, of the first line is placed at the same distance from the row grid. In addition, at least, one of these first child areas of the cells has to be placed with the before-edge of its allocation-rectangle coincident with the before-edge of the content-rectangle of the table-cell.

NOTE: 

That is, for all applicable cells the baseline of all the first lines are all aligned and placed the minimum distance down in the block-progression-direction. It should be noted that the start-edges of the content-rectangles of the cells need not align.

For an fo:list-item the distance between the baseline of the first line-area of the first area descendant generated by the fo:list-item-label is the same as the distance between the baseline of the first line-area of the first area descendant generated by the fo:list-item-body. In addition, at least, one of these first area descendants has to be placed such that the before-edge of its allocation-rectangle is coincident with the before-edge of the content-rectangle of the list-item.