Comparison of vertical and horizontal Japanese: iBunko application (iOS)
CSS3 Writing Modes defines CSS features to support for various international writing modes, such as left-to-right (e.g. Latin or Indic), right-to-left (e.g. Hebrew or Arabic), bidirectional (e.g. mixed Latin and Arabic) and vertical (e.g. Asian scripts).
Inherently bottom-to-top scripts are not handled in this version. See [[UTN22]] for an explanation of relevant issues.
CSS3 Writing Modes defines CSS features to support for various international writing modes, such as left-to-right (e.g. Latin or Indic), right-to-left (e.g. Hebrew or Arabic), bidirectional (e.g. mixed Latin and Arabic) and vertical (e.g. Asian scripts).
A writing mode in CSS is determined by the 'writing-mode', 'direction', and 'text-orientation' properties. It is defined primarily in terms of its inline base direction and block flow direction:
The inline base direction is the primary direction in which content is ordered on a line and defines on which sides the "start" and "end" of a line are. The 'direction' property specifies the inline base direction of an element and, together with the 'unicode-bidi' property and the inherent directionality of any text content, determines the ordering of inline-level content within a line.
The block flow direction is the direction in which block-level boxes stack and the direction in which line boxes stack within a block container. The 'writing-mode' property determines the block flow direction.
A horizontal writing mode is one with horizontal lines of text, i.e. a downward or upward block flow. A vertical writing mode is one with vertical lines of text, i.e. a leftward or rightward block flow.
These terms should not be confused with vertical block flow (which is a downward or upward block flow) and horizontal block flow (which is leftward or rightward block flow). To avoid confusion, the CSS specifications avoid this latter set of terms.
Writing systems typically have one or two native writing modes. Some examples are:
See Unicode Technical Note #22 [[UTN22]] (HTML version) for a more in-depth introduction to writing modes and vertical text.
Point at Intro to Text Orientaiton section once it's written.
While the characters in most scripts are written from left to right, certain scripts are written from right to left. In some documents, in particular those written with the Arabic or Hebrew script, and in some mixed-language contexts, text in a single (visually displayed) block may appear with mixed directionality. This phenomenon is called bidirectionality, or "bidi" for short.
.manokim rak W3C ab nam <---------- --> <-----
Bidirectionality
The Unicode standard (Unicode Standard Annex #9) defines a complex algorithm for determining the proper ordering of bidirectional text. The algorithm consists of an implicit part based on character properties, as well as explicit controls for embeddings and overrides. CSS relies on this algorithm to achieve proper bidirectional rendering. The 'direction' and 'unicode-bidi' properties allow authors to specify how the elements and attributes of a document language map to this algorithm.
User agents that support bidirectional text must apply the Unicode bidirectional algorithm to every sequence of inline boxes uninterrupted by a forced (bidi class B) line break or block boundary. This sequence forms the "paragraph" unit in the bidirectional algorithm. The paragraph embedding level is set according to the value of the 'direction' property of the containing block rather than by the heuristic given in steps P2 and P3 of the Unicode algorithm.
Because the base directionality of a text depends on the structure and semantics of the document, these properties should in most cases be used only to map bidi information in the markup to its corresponding CSS styles. If a document language provides markup features to control bidi, authors and users should use those features and not specify CSS rules to override them.
The HTML 4 specification ([[HTML401]], section 8.2) defines bidirectionality behavior for HTML elements. The HTML 4 specification also contains more information on bidirectionality issues.
Because HTML UAs can turn off CSS styling, we advise HTML authors to use the HTML 'dir' attribute and <bdo> element to ensure correct bidirectional layout in the absence of a style sheet.
| Name: | direction |
|---|---|
| Value: | ltr | rtl |
| Initial: | ltr |
| Applies to: | all elements |
| Inherited: | yes |
| Percentages: | N/A |
| Media: | visual |
| Computed value: | specified value |
This property specifies the base directionality of text and elements on a line, and the directionality of embeddings and overrides (see 'unicode-bidi') for the Unicode bidirectional algorithm. In addition, it affects the ordering of table column layout, the direction of horizontal overflow, and the default alignment of text within a line, and other things that depend on the base inline base direction.
Values for this property have the following meanings:
The 'direction' property has no reordering in inline-level elements whose 'unicode-bidi' property's value is ''normal''.
The value of the 'direction' property on the root element is also propagated to the initial containing block and, together with the 'writing-mode' property, determines the document's principal writing mode. (See below.)
Note that the 'direction' property of the HTML BODY element is not propagated to the viewport. That special behavior only applies to the background and overflow properties.
The 'direction' property, when specified for table column elements, is not inherited by cells in the column since columns are not the ancestors of the cells in the document tree. Thus, CSS cannot easily capture the "dir" attribute inheritance rules described in [[HTML401]], section 11.3.2.1.
| Name: | unicode-bidi |
|---|---|
| Value: | normal | [ [ embed | isolate ] || [ plaintext | bidi-override ] ] |
| Initial: | normal |
| Applies to: | all elements, but see prose |
| Inherited: | no |
| Percentages: | N/A |
| Media: | visual |
| Computed value: | specified value |
Values for this property have the following meanings:
For the purposes of the Unicode bidirectional algorithm, the base directionality of each "paragraph" for which the element is the containing block element is determined not by the element's computed 'direction' as usual, but by following rules P1, P2, and P3 of the Unicode bidirectional algorithm. However, if no direction-determining character is found in step P2, then the value of the 'direction' property is used instead. Note this value has no effect on inline elements.
The final order of characters in each block-level element is the same as if the bidi control codes had been added as described above, markup had been stripped, and the resulting character sequence had been passed to an implementation of the Unicode bidirectional algorithm for plain text that produced the same line-breaks as the styled text. In this process, non-textual entities such as images are treated as neutral characters, unless their 'unicode-bidi' property has a value other than 'normal', in which case they are treated as strong characters in the 'direction' specified for the element.
Please note that in order to be able to flow inline boxes in a uniform direction (either entirely left-to-right or entirely right-to-left), more inline boxes (including anonymous inline boxes) may have to be created, and some inline boxes may have to be split up and reordered before flowing.
Because the Unicode algorithm has a limit of 61 levels of embedding, care should be taken not to use 'unicode-bidi' with a value other than 'normal' unless appropriate. In particular, a value of 'inherit' should be used with extreme caution. However, for elements that are, in general, intended to be displayed as blocks, a setting of 'unicode-bidi: isolate' is preferred to keep the element together in case display is changed to inline (see example below).
The following example shows an XML document with bidirectional text. It illustrates an important design principle: document language designers should take bidi into account both in the language proper (elements and attributes) and in any accompanying style sheets. The style sheets should be designed so that bidi rules are separate from other style rules, and such rules should not be overridden by other style sheets so that the document language's bidi behavior is preserved.
In this example, lowercase letters stand for inherently left-to-right characters and uppercase letters represent inherently right-to-left characters. The text stream is shown in logical backing store order.
<HEBREW>
<PAR>HEBREW1 HEBREW2 english3 HEBREW4 HEBREW5</PAR>
<PAR>HEBREW6 <EMPH>HEBREW7</EMPH> HEBREW8</PAR>
</HEBREW>
<ENGLISH>
<PAR>english9 english10 english11 HEBREW12 HEBREW13</PAR>
<PAR>english14 english15 english16</PAR>
<PAR>english17 <HE-QUO>HEBREW18 english19 HEBREW20</HE-QUO></PAR>
</ENGLISH>
Since this is arbitrary XML, the style sheet is responsible for setting the writing direction. This is the style sheet:
/* Rules for bidi */
HEBREW, HE-QUO {direction: rtl; unicode-bidi: embed;}
ENGLISH {direction: ltr; unicode-bidi: embed;}
/* Rules for presentation */
HEBREW, ENGLISH, PAR {display: block;}
EMPH {font-weight: bold;}
The HEBREW element is a block with a right-to-left base direction, the ENGLISH element is a block with a left-to-right base direction. The PARs are blocks that inherit the base direction from their parents. Thus, the first two PARs are read starting at the top right, the final three are read starting at the top left. Please note that HEBREW and ENGLISH are chosen as element names for explicitness only; in general, element names should convey structure without reference to language.
The EMPH element is inline-level, and since its value for 'unicode-bidi' is 'normal' (the initial value), it has no effect on the ordering of the text. The HE-QUO element, on the other hand, creates an embedding.
The formatting of this text might look like this if the line length is long:
5WERBEH 4WERBEH english3 2WERBEH 1WERBEH
8WERBEH 7WERBEH 6WERBEH
english9 english10 english11 13WERBEH 12WERBEH
english14 english15 english16
english17 20WERBEH english19 18WERBEH
Note that the HE-QUO embedding causes HEBREW18 to be to the right of english19.
If lines have to be broken, it might be more like this:
2WERBEH 1WERBEH
-EH 4WERBEH english3
5WERB
-EH 7WERBEH 6WERBEH
8WERB
english9 english10 en-
glish11 12WERBEH
13WERBEH
english14 english15
english16
english17 18WERBEH
20WERBEH english19
Because HEBREW18 must be read before english19, it is on the line above english19. Just breaking the long line from the earlier formatting would not have worked. Note also that the first syllable from english19 might have fit on the previous line, but hyphenation of left-to-right words in a right-to-left context, and vice versa, is usually suppressed to avoid having to display a hyphen in the middle of a line.
For each line box, UAs must take the inline boxes generated for each element and render the margins, borders and padding in visual order (not logical order).
When the element's 'direction' property is ''ltr'', the left-most generated box of the first line box in which the element appears has the left margin, left border and left padding, and the right-most generated box of the last line box in which the element appears has the right padding, right border and right margin.
When the element's 'direction' property is ''rtl'', the right-most generated box of the first line box in which the element appears has the right padding, right border and right margin, and the left-most generated box of the last line box in which the element appears has the left margin, left border and left padding.
In addition to extensions to CSS2.1's support for bidirectional text, this module introduces the rules and properties needed to support vertical text layout in CSS.
Unlike languages that use the Latin script which are primarily laid out horizontally, Asian languages such as Chinese and Japanese can be laid vertically. The Japanese example below shows the same text laid out horizontally and vertically. In the horizontal case, text is read from left to right, top to bottom. For the vertical case, the text is read top to bottom, right to left. Indentation from the left edge in the left-to-right horizontal case translates to indentation from the top edge in the top-to-bottom vertical case.
Comparison of vertical and horizontal Japanese: iBunko application (iOS)
For Chinese and Japanese lines are ordered either right to left, while for Mongolian and Manchu left to right.
The change from horizontal to vertical writing can affect not just the layout, but also the typesetting. For example, the position of a punctuation mark within its spacing box can change from the horizontal to the vertical case, and in some cases alternate glyphs are used.
Vertical text that includes Latin script text or text from other scripts normally displayed horizontally can display that text in a number of ways. For example, Latin words can be rotated sideways, or each letter can be oriented upright:
Examples of Latin in vertical Japanese: Daijirin Viewer 1.4 (iOS)
In some special cases such as two-digit numbers in dates, text is fit compactly into a single vertical character box:
Mac Fan, December 2010, p.49
Layouts often involve a mixture of vertical and horizontal elements:
Mixture of vertical and horizontal elements
Vertical text layouts also need to handle bidirectional text layout; clockwise-rotated Arabic, for example, is laid out bottom-to-top.
| Name: | writing-mode |
|---|---|
| Value: | horizontal-tb | vertical-rl | vertical-lr |
| Initial: | horizontal-tb |
| Applies to: | All elements except table row groups, table column groups, table rows, and table columns |
| Inherited: | yes |
| Percentages: | N/A |
| Media: | visual |
| Computed value: | specified value |
This property sets the block flow direction. Possible values:
SVG1.1 [[!SVG11]] defines some additional values: ''lr'', ''lr-tb'', ''rl'', ''rl-tb'', ''tb'', and ''tb-rl''. These values are deprecated in any context except SVG1 documents. Implementations that wish to support them in the context of CSS must treat these values as follows:
| SVG1 | CSS |
|---|---|
| lr | horizontal-tb |
| lr-tb | |
| rl | |
| tb | vertical-rl |
| tb-rl |
In SVG1.1, these values set the inline progression direction, in other words, the direction the current text position advances each time a glyph is added. This is a geometric process that happens after bidi reordering, and thus has no effect on the interpretation of the 'direction' property (which is independent of 'writing-mode'). (See Relationship with bidirectionality. [[!SVG11]]) There are varying interpretations on whether this process causes "writing-mode: rl" to merely shift the text string or reverse the order of all glyphs in the text.
See this demo to check out your implementation's interpretation! (Note that most SVG implementations don't support the 'direction' property, and thus your results may be skewed on that account. Examine the red line of text: if the numbers are not in reverse order, your implementation doesn't support "direction: rtl".)
The 'writing-mode' property determines the direction of block flow. This determines the progression of block-level boxes in a block formatting context; the progression of line boxes in a block container that contains inlines; and the progression of rows in a table. By virtue of determining the stacking direction of line boxes, the 'writing-mode' property also determines whether line boxes and thus the writing mode is horizontal or vertical.
When set on the root element, the 'writing-mode' property together with the 'direction' property determines the principal writing mode of the document. This writing mode is used, for example, to determine the default page progression direction. (See [[CSS3PAGE]].) The 'writing-mode' value of the root element is also propagated to the initial containing block and sets the block flow direction of the initial block formatting context.
Note that the 'writing-mode' property of the HTML BODY element is not propagated to the viewport. That special behavior only applies to the background and overflow properties.
If an element has a different block flow direction than its containing block:
If such an element is a block container, then it establishes a new block formatting context.
The content of replaced elements do not rotate due to the writing mode: images, for example, remain upright. However replaced content involving text (such as MathML content or form elements) should match the replaced element's writing mode and line orientation if the UA supports such a vertical writing mode for the replaced content.
In the following example, two blocks elements (1 and 3) separated by an image (2) are presented in various flow writing modes.
Here is a diagram of horizontal writing mode (writing-mode: horizontal-tb):
Here is a diagram for the right-to-left vertical writing mode commonly
used in East Asia (writing-mode: vertical-rl):
And finally, here is a diagram for the left-to-right vertical
writing mode used for Manchu and Mongolian (writing-mode: vertical-lr):
[Describe here any necessary concepts from UTN22]
| Name: | text-orientation |
|---|---|
| Value: | vertical-right | upright | rotate-right | rotate-left | rotate-normal | auto |
| Initial: | vertical-right |
| Applies to: | all elements except table row groups, rows, column groups, and columns |
| Inherited: | yes |
| Percentages: | N/A |
| Media: | visual |
| Computed value: | specified value |
This property specifies the orientation of characters within a line and sets the orientation of the line. Current values only have an effect in vertical writing modes. Values have the following meanings:
In vertical writing modes, grapheme clusters from scripts that do not have an intrinsic vertical orientation are rotated 90° clockwise from their standard orientation in horizontal text. Characters from scripts that do have an intrinsic vertical orientation are set in that orientation. When available, vertical glyph variants and vertical font metrics are used to set all punctuation and characters from any script that is not rotated. In vertical writing modes, this value puts the UA in a vertical typographic mode and is typical for layout of primarily vertical-script text.
In vertical writing modes, grapheme clusters that do not have an intrinsic vertical orientation are rendered upright, i.e. in their standard horizontal orientation. Shaping characters from such scripts are shaped in their isolated forms. Characters from scripts that do have an intrinsic vertical orientation are set in that orientation. When available, vertical glyph variants and vertical font metrics are used to set the text. The UA should synthesize vertical font metrics for grapheme clusters that do not have any.
For the purposes of bidi reordering, this value causes all characters to be treated as strong LTR. This value causes the used value of 'direction' to be ''ltr''.
In vertical writing modes, this value puts the UA in a vertical typographic mode.
In vertical writing modes, this causes text to be set as if in a horizontal layout (using horizontal glyph variants and metrics), but rotated 90° clockwise. This value puts the UA in a This value puts the UA in a horizontal typographic mode and can be used for ''vertical-rl'' text in a primarily horizontal-script document.
In vertical writing modes, this causes text to be set as if in a horizontal layout (using horizontal glyph variants and metrics), but rotated 90° counter-clockwise. This value puts the UA in a horizontal typographic mode and can be used for ''vertical-lr'' text in a primarily horizontal-script document.
If set on a non-replaced inline whose parent is not ''rotate-left'', this forces ''isolate'' to be added to the computed value of 'unicode-bidi'. Layout of text is exactly as for ''rotate-right'' except that the entire text content and baseline table of the element is mirrored: each box of the inline is mirrored around a vertical axis such that its content box does not move. (However the contents of atomic inlines are not mirrored; only their alignment is changed.) Similarly, if a child of the element has a 'text-orientation' value other than ''rotate-left'', an analogous transformation is applied.
This value is equivalent to ''rotate-right'' in ''vertical-rl'' writing mode and equivalent to ''rotate-left'' in ''vertical-lr'' writing mode.
[[!SVG11]] defines 'glyph-orientation-vertical' and 'glyph-orientation-horizontal' properties that were intended to control text orientation. These properties are deprecated and do not apply to non-SVG elements. If an implementation supports these properties, the ''auto'' value when set on SVG elements indicates that the SVG 'glyph-orientation-vertical' and 'glyph-orientation-horizontal' behavior control the layout of text. Such UAs must set ''text-orientation: auto'' on all SVG text content elements in their default UA style sheet for SVG.
In all other contexts, and for implementations that do not support the glyph orientation properties, the ''auto'' behavior is the same as for ''vertical-right''.
text-orientation: vertical-right, upright, rotate-left, and rotate-right
Baseline alignment is not yet defined.
Add section explaining native script orientations. Note that all wide characters are treated the same as ideographic. Link to definition of grapheme clusters in [[!UAX29]].
Add appendix that describes interaction with OpenType features and font layout?
[[!CSS21]] defines the box layout model of CSS in detail. However, it only defines the box model for the ''horizontal-tb'' writing mode. CSS box layout in writing modes other than ''horizontal-tb'' is analogous to the box layout defined in CSS2.1 if directions and dimensions are abstracted and remapped appropriately. This section defines abstract directional and dimensional terms and their mappings in order to define box layout for other writing modes, and to provide terminology for future specs to define their layout concepts abstactly.
The terms left, right, top, and bottom are always interpreted physically, i.e. with respect to the page independent of writing mode. Two abstract mappings are possible for these directions: line-relative and flow-relative, which are defined below.
Although they derive from the behavior of text, these directional terms exist even for boxes that do not contain any line boxes: they are calculated directly from the values of the 'writing-mode', 'text-orientation', and 'direction' properties.
Although the block flow direction given by 'writing-mode' determines whether the line is oriented horizontally or vertically, it doesn't say anything about how the contents within the line are arranged.
The line orientation determines which side of the line is the "top" and thus which sides are under (ascender side) and over (descender side) the line. This determines the interpretation of alignment in the transverse dimension of the line. It also determines the default glyph orientation for scripts in a non-native orientation. These characteristics are controlled by the 'text-orientation' property.
In addition to its over and under sides, a line box, even a vertically-oriented one, also has a "left" and "right" side, which we will call the line-left and line-right sides of the box (as distinct from the physical left and physical right sides of the box). The line-left edge of a box is nominally the edge from which LTR text would start. The line-right edge of a box is nominally the edge from which RTL text would start. Depending on the 'writing-mode' and 'text-orientation' properties, the line-left side of a box could be on the left, top, or bottom.
Line orientation compass
Typical orientation in vertical
Line orientation with ''text-orientation: rotate-left''
Note also that while the over and under directions often map to the same directions as before and after respectively, this mapping is reversed for some combinations of 'writing-mode' and 'text-orientation'.
The flow-relative directions are before, after, start, and end. In an LTR ''horizontal-tb'' writing mode, they correspond to the top, bottom, left, and right directions, respectively.
The before edge of a box is nominally the edge that comes earlier in the block progression, as determined by the 'writing-mode' poperty. Similarly the after edge is the edge that comes later in the progression.
The start edge of a box is nominally the edge from which text of its inline base direction will start. For boxes with a used 'direction' value of ''ltr'', this means the line-left edge. For boxes with a used 'direction' value of ''rtl'', this means the line-right edge. The edge opposite the start edge is the end edge.
Note that while determining the before and after edges of a box depends only on the 'writing-mode' property, determining the start and end edges of a box depends not only on the 'writing-mode' property but also the 'direction' and 'text-orientation' properties.
An English (LTR-TB) block:
<----- width / measure ----->
top side/
before side
+------------------------------+ A
left side/ | ---inline direction ---> | right side/ |
start side | | | end side |
| | block * horizontal * | height/
| | direction *writing mode* | length
| V | |
+------------------------------+ V
bottom side/
after side
A vertical Japanese block (TTB-RL):
<----- width / length ------>
top side/
start side
+------------------------------+ A
left side/ | <---block direction--- | right side/ |
after side | | | before side |
| * vertical * inline| | height/
| *writing mode* direction| | measure
| V | |
+------------------------------+ V
bottom side/
end side
The following table summarizes the abstract-to-physical mappings:
| 'writing-mode' | ''horizontal-tb'' | ''vertical-rl'' | ''vertical-lr'' | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 'text-orientation' | — | ''rotate-left'' | *right | ''rotate-left'' | *right | |||||
| 'direction' | ''ltr'' | ''rtl'' | ''ltr'' | ''rtl'' | ''ltr'' | ''rtl'' | ''ltr'' | ''rtl'' | ''ltr'' | ''rtl'' |
| length | height | width | ||||||||
| measure | width | height | ||||||||
| before | top | right | left | |||||||
| after | bottom | left | right | |||||||
| start | left | right | bottom | top | top | bottom | bottom | top | top | bottom |
| end | right | left | top | bottom | bottom | top | top | bottom | bottom | top |
| over | top | left | right | left | right | |||||
| under | bottom | right | left | right | left | |||||
| line-left | left | bottom | top | bottom | top | |||||
| line-right | right | top | bottom | top | bottom | |||||
CSS box layout in vertical writing modes is analogous to layout in the horizontal writing modes, following the principles outlined below:
Layout calculation rules (such as those in CSS2.1, Section 10.3) that apply to the horizontal dimension in horizontal writing modes instead apply to the vertical dimension in vertical writing modes. Likewise, layout calculation rules (such as those in CSS2.1, Section 10.6) that apply to the vertical dimension in horizontal writing modes instead apply to the horizontal dimension in vertical writing modes. Thus:
Layout rules that refer to the width use the height instead, and vice versa.
Layout rules that refer to the '*-left' and '*-right' box properties (border, margin, padding) use '*-top' and '*-bottom' instead, and vice versa.
Which side of the box the property applies to doesn't change: only which values are inputs to which layout calculations changes. The 'margin-left' property still affects the lefthand margin, for example; however in a ''vertical-rl'' writing mode it takes part in margin collapsing in place of 'margin-bottom'.
Layout rules that depend on the 'direction' property to choose between left and right (e.g. overflow, overconstraint resolution, the initial value for 'text-align', table column ordering) are abstracted to the start and end sides and applied appropriately.
For features such as text alignment, floating, and list marker positioning, that primarily reference the left or right sides of the line box or its longitudinal parallels and therefore have no top or bottom equivalent, the line left and line right sides are used as the reference for the left and right sides respectively.
Likewise for features such as underlining, overlining, and baseline alignment (the unfortunately-named 'vertical-align'), that primarily reference the top or bottom sides of the linebox or its transversal parallels and therefore have no left or right equivalent, the over and under sides are used as the reference for the top and bottom sides respectively.
The details of these mappings are provided below.
Certain properties behave logically as follows:
The height properties ('height', 'min-height', and 'max-height') refer to the physical height, and the width properties ('width', 'min-width', and 'max-width') refer to the physical width. However, the rules used to calculate box dimensions and positions are logical.
For example, the calculation rules in CSS2.1 Section 10.3 are used for the inline dimension measurements: they apply to the measure (which could be either the physical width or physical height) and to the the start and end margins, padding, and border. Likewise the calculation rules in CSS2.1 Section 10.6 are used in the block dimension: they apply to the length and to the before and after margins, padding, and border. [[!CSS21]]
As a corollary, percentages on the margin and padding properties, which are always calculated with respect to the containing block width in CSS2.1, are calculated with respect to the measure of the containing block in CSS3.
When an element has a different 'writing-mode' from its containing block two cases are possible:
To handle the second case, for the purposes of calculating the layout of the box, the physical dimensions corresponding to the length and measure of the containing block are determined using the writing mode of the box under consideration, not the writing mode of the element associated with the containing block.
For example, if a vertical block is placed inside a horizontal block, then when calculating the physical height (which is the measure) of the child block the physical height of the parent block is used to calculate the measure of the child's containing block, even though the physical height is the length, not the measure, of the parent block.
It is common in CSS for a containing block to have a defined measure, but not a defined length. This typically happens in CSS2.1 when a containing block has an ''auto'' height, for example: its width is given by the calculations in 10.3.3, but its length depends on its contents. In such cases the available measure is defined, but the available length is infinite.
Orthogonal flows allow the opposite to happen: for the available length to be defined, but the available measure to be infinite. In such cases a percentage of the containing block measure cannot be defined, and thus the initial containing block's measure is used to calculate such percentages instead. Is this definition of percentages a good idea?
If the computed measure of an element establishing an orthogonal flow is ''auto'', then the used measure is calculated as the shrink-to-fit (''fit-content'') value using the initial containing block's measure as the available size in the shrink-to-fit algorithm.
As with other shrink-to-fit boxes, the width and height calculations occur before auto margin calculations in the inline dimension, and therefore a block box establishing an orthogonal flow, once sized, can be aligned or centered within its containing block just like other block-level elements by using auto margins.
If the UA supports CSS Multi-column Layout [[!CSS3COL]], then for the case where the available length is defined but the available measure is infinite and the element's measure is unconstrained (is not fixed and has no maximum):
This section is informative.
With regards to pagination, the rules in CSS2.1 still hold in vertical writing modes and orthogonal flows: page break opportunities do not occur inside line boxes, only between them. Note that UAs that support [[!CSS3COL]] may break between columns, however. Does CSS3 Multicol specify this as requested?
Note that if content spills outside the pagination stream established by the root element, the UA is not required to print such content. Authors wishing to mix writing modes with long streams of text are thus encouraged to use CSS columns to keep all content flowing in the document's pagination direction.
In other words, if your document would require two scrollbars on the screen it probably won't all print. Fix your layout, e.g. by using columns so that it all scrolls (and therefore paginates) in one direction if you want to make sure it'll all print. T-shaped documents tend not to print well.
Flow-relative directions are calculated with respect to the writing mode of the element and used to abstract layout related to padding and border properties. For example, if an element had computed values of ''direction: ltr; writing-mode: vertical-lr; text-orientation: vertical-right'', 'padding-top' would give its start padding, and 'padding-left' would give its before padding.
Flow-relative directions are calculated with respect to the writing mode of the parent of the element and used to abstract layout related to the margin properties and the 'top', 'bottom', 'left', and 'right' properties. (For the root element, which has no parent, the values of the writing mode of the element is used instead.)
The margin collapsing rules apply exactly with the before margin substituted for the top margin and the after margin substituted for the bottom margin. Similarly the padding and border on the same side as the before margin is substituted for the top padding and border, and the padding and border on the same side as the after margin for the bottom padding and border. Note this means only before and after margins ever collapse.
The parent element is used instead of the containing block, because the benefit of using the containing block is very rare, but the cost to implement it is rather high for implementations that do abstract-physical mapping at cascade time.
The start and end directions are also used for inline layout as follows:
The line-relative directions are over, under, line-left, and line-right. In an LTR ''horizontal-tb'' writing mode, they correspond to the top, bottom, left, and right directions, respectively.
The line-right and line-left directions are calculated with respect to the writing mode of the element and used to interpret the ''left'' and ''right'' values of the following properties:
The line-right and line-left directions are calculated with respect to the writing mode of the containing block of the element and used to interpret the ''left'' and ''right'' values of the following properties:
The over and under directions are calculated with respect to the writing mode of the element and used to define the interpretation of the "top" (over edge) and "bottom" (under edge) of the line box as follows:
The following values are purely physical in their definitions and do not respond to changes in writing mode:
This module introduces two new values to the 'caption-side' property: ''before'' and ''after'', which position the caption before and after the table box, respectively. For tables with ''horizontal-tb'' writing mode, they are equivalent to the existing ''top'' and ''bottom'' values, respectively. [[!CSS21]]
Implementations that support the ''top'' and ''bottom'' values of the 'caption-side' property but do not support side captions (i.e. ''left'' and ''right'' captions in horizontal writing modes) must treat ''top'' and ''bottom'' as ''before'', when the table is in a vertical writing mode.
For implementations that do support side captions (i.e. the ''left'' and ''right'' values), this module also introduces the ''start'' and ''end'' values, which behave similarly and which position the caption on the start and end sides of the table box, calculated with respect to the writing mode of the table element. For such implementations, the ''top'' and ''bottom'' values must place the caption on the top and bottom sides of the table box, respectively.
| Name: | text-combine |
|---|---|
| Value: | none | [ horizontal <number>? ] |
| Initial: | none |
| Applies to: | non-replaced inline elements |
| Inherited: | no |
| Percentages: | N/A |
| Media: | visual |
| Computed value: | specified value |
This property allows the combination of multiple characters into the space of a single character. For text layout purposes, e.g. bidi ordering, line-breaking, emphasis marks, text-decoration, etc. the resulting composition is treated as a single glyph representing the Object Replacement Character U+FFFC. Values have the following meanings:
In vertical writing mode, attempt to display the text contents of the element horizontally within the vertical line box, ideally within the space of one ideographic character (1em square).
The glyphs are stacked horizontally (similar to the contents of an inline-box with a horizontal writing mode and a line-height of 1em) and the baseline of the resulting composition chosen such that it is centered between the content edges of its parent inline box.
The UA should determine how to render the composed glyph into the space. If the UA has compressed glyphs available for the contents of the element, then it may use those glyphs to attempt sizing the contents to 1em square. For example, a two digit number may use halfwidth or proportional glyphs, a three-digit number may use 1/3-em glyphs (if available, else halfwidth glyphs), etc.
The UA may scale the contents to fit instead, or in addition to the method above.
In horizontal mode, or if the number of grapheme clusters in the element exceeds the number specified (if any), this value is equivalent to ''none''.
In East Asian documents, the ''text-combine: horizontal'' effect is often used to display Latin-based strings such as components of a date or letters of an initialism, always in a horizontal writing mode regardless of the writing mode of the line:
Example of horizontal-in-vertical tate-chu-yoko
The figure is the result of the rules
.num { text-combine: horizontal; }
and the following markup:
平成<span class="num">20</span>年
<span class="num">4</span>月
<span class="num">16</span>日に
In Japanese, this effect is known as tate-chu-yoko.
Some people have requested a way to have numbers automatically text-combine'd. Maybe a text-auto-combine property? Note that whether a number should be tate-chu-yoko'd is often context-sensitive: this would give very weird results when applied to an arbitrary paragraph.
John Daggett, Martin Heijdra, Paul Nelson, Michel Suignard, Steve Zilles
The style sheet rules that would achieve the bidi behaviors specified in [[HTML401]] for the HTML Strict doctype are given below:
/* HTML dir attribute creates an embedding */
*[dir="ltr"] { direction: ltr; unicode-bidi: embed; }
*[dir="rtl"] { direction: rtl; unicode-bidi: embed; }
/* BDO element creates an override */
bdo[dir="ltr"] { direction: ltr; unicode-bidi: bidi-override; }
bdo[dir="rtl"] { direction: rtl; unicode-bidi: bidi-override; }
/* HTML4.01:8.2.6 - preserve bidi behavior if 'display' is changed */
html, body,
div, address, blockquote, p,
ul, ol, li, dl, dt, dd,
fieldset, form,
h1, h2, h3, h4, h5, h6,
{ unicode-bidi: isolate; }