1. Introduction
This module defines the CSS Inline Layout model, replacing and extending the model as defined in CSS2.1. It is very much a work-in-progress, and implementers should reference CSS2.1 for now.
The root inline box is an anonymous inline box which is automatically generated to hold all of the inline-level contents of a block container (if it has any). It inherits from its parent block container, but is otherwise unstyleable.
Note: Line boxes, like column boxes [css-multicol-1], are fragmentation containers generated by their formatting context and are not part of the CSS box tree.
Many aspects of layout here depend on font metrics. While the relevant metrics exist in OpenType for Latin/Cyrillic/Greek and for CJK, they are missing for many other writing systems. For example, the visual top metric for Hebrew has no metric in the OpenType tables. For this module to work well for the world, we need fonts to provide the relevant metrics for all writing systems, and that means both that OpenType needs to allow such metrics and font designers need to provide accurate numbers.
2. Line Heights and Baseline Alignment
This section is being rewritten. Refer to section 10.8 of [CSS2] for the normative CSS definition or the 2002 Working Draft if you want pretty pictures. (But ignore the old text, half of it’s wrong. We’re not specifying which half, that’s to be determined.) The CSS2 specification should be used as the guideline for implementation.
The CSSWG would like to know which baseline values are necessary: if any can be dropped, or any need to be added. See GitHub issue 859.
2.1. Dominant Baselines: the dominant-baseline property
Name: | dominant-baseline |
---|---|
Value: | auto | text-bottom | alphabetic | ideographic | middle | central | mathematical | hanging | text-top |
Initial: | normal |
Applies to: | block containers, inline boxes, table rows, table columns, grid containers, and flex containers |
Inherited: | yes |
Percentages: | N/A |
Computed value: | specified keyword |
Canonical order: | per grammar |
Animation type: | discrete |
This property specifies the dominant baseline, which is the baseline used to align the box’s text and inline-level contents. It is also indicates the default alignment baseline of any boxes participating in baseline alignment in the box’s alignment context. Values have the following meanings:
- auto
-
Equivalent to alphabetic in horizontal writing modes and in vertical writing modes when text-orientation is sideways, sideways-right, or sideways-left.
Equivalent to central in vertical writing modes when text-orientation is mixed or upright.
However, in SVG text, the origin point of glyphs (used for coordinate-based glyph positioning) is always handled as for central in vertical writing modes.
- text-bottom
- Use the bottom of the em box as the baseline.
- alphabetic
- Use the alphabetic baseline.
- ideographic
- Match the box’s ideographic under-side baseline to that of its parent.
This corresponds to the
ideo
baseline in OpenType. - middle
- Use the “middle” baseline: halfway between the alphabetic baseline and the ex-height.
- central
- Use the central baseline (halfway between the ascent and descent).
- mathematical
- Use the mathematical baseline.
- hanging
- Use the hanging baseline.
- text-top
- Use the top of the em box as the baseline.
See [CSS-WRITING-MODES-3] for an introduction to dominant baselines.
Should be text-over and text-under instead of text-top and text-bottom, but maybe it’s better not to use those terms for consistency with legacy vertical-align. See GitHub issue 860.
Add first and last values. Note, in this property, these are combinatorial, whereas in the align/justify-self/content properties, it’s singular. Do we want to align the syntaxes wrt hyphens vs. spaces or what? See GitHub issue 861.
2.2. Transverse Box Alignment: the vertical-align property
Name: | vertical-align |
---|---|
Value: | <‘baseline-shift’> || <‘alignment-baseline’> |
Initial: | baseline |
Applies to: | inline-level boxes |
Inherited: | no |
Percentages: | N/A |
Computed value: | see individual properties |
Animation type: | see individual properties |
Canonical order: | per grammar |
This shorthand property specifies how an inline-level box is aligned within the line. Values are the same as for its longhand properties, see below.
Authors should use this property (vertical-align) instead of its longhands.
This property will gain first and last keywords, like in the box alignment properties, see CSS Box Alignment 3 §4.2 Baseline Alignment: the baseline keyword and first/last modifiers. The open question is whether they should be added to alignment-baseline or a new sub-property should be created to hold the first | last preference.
2.2.1. Alignment Point: alignment-baseline longhand
Name: | alignment-baseline |
---|---|
Value: | baseline | text-bottom | alphabetic | ideographic | middle | central | mathematical | text-top | bottom | center | top |
Initial: | baseline |
Applies to: | inline-level boxes, flex items, grid items, table cells |
Inherited: | no |
Percentages: | N/A |
Computed value: | specified keyword |
Canonical order: | per grammar |
Animation type: | discrete |
Specifies what point of an inline-level box is aligned to what point in the parent. Also selects the alignment baseline of boxes aligned with align-self/justify-self.
Clean up this prose to correctly handle alignment contexts other than inline formatting contexts.
Values are defined below:
For the following definitions, the margin box is used for atomic inlines, the leading box for non-replaced inlines, and the baselines of the box are synthesized if missing in the line-box’s inline axis:
- baseline
- Use the dominant baseline choice of the parent. Match the box’s corresponding baseline to that of its parent.
- text-bottom
- Match the bottom of the box to the bottom of the parent’s content area.
- alphabetic
- Match the box’s alphabetic baseline to that of its parent.
- ideographic
- Match the box’s ideographic character face under-side baseline to that of its parent.
- middle
- Align the vertical midpoint of the box with the baseline of the parent box plus half the x-height of the parent.
- central
- Match the box’s central baseline to the central baseline of its parent.
- mathematical
- Match the box’s mathematical baseline to that of its parent.
- text-top
- Match the top of the box to the top of the parent’s content area.
For the following definitions, the alignment subtree is as defined in [CSS2].
- top
- Align the top of the aligned subtree with the top of the line box.
- center
- Align the center of the aligned subtree with the center of the line box.
- bottom
- Align the bottom of the aligned subtree with the bottom of the line box.
SVG implementations may support the following aliases in order to support legacy content:
text-before-edge = text-top text-after-edge = text-bottom
These values are not allowed in the vertical-align shorthand.
2.2.2. Alignment Shift: the baseline-shift longhand
Name: | baseline-shift |
---|---|
Value: | <length-percentage> | sub | super |
Initial: | 0 |
Applies to: | inline-level boxes, flex items, grid items |
Inherited: | no |
Percentages: | refer to the used value of line-height |
Computed value: | the specified keyword and/or a computed <length-percentage> value |
Canonical order: | per grammar |
Animation type: | discrete |
This property specifies by how much the box is shifted up from its alignment point. It does not apply when alignment-baseline is top or bottom.
Authors should use the vertical-align shorthand instead of this property.
Values have the following meanings:
- <length>
- Raise (positive value) or lower (negative value) by the specified length.
- <percentage>
- Raise (positive value) or lower (negative value) by the specified percentage of the line-height.
- sub
- Lower by the offset appropriate for subscripts of the parent’s box. (The UA should use the parent’s font data to find this offset whenever possible.)
- super
- Raise by the offset appropriate for superscripts of the parent’s box. (The UA should use the parent’s font data to find this offset whenever possible.)
User agents may additionally support the keyword baseline as computing to 0 if is necessary for them to support legacy SVG content.
We would prefer to remove this, and are looking for feedback from SVG user agents as to whether it’s necessary.
2.3. Line Spacing: the line-height property
Name: | line-height |
---|---|
Value: | normal | <number> || <length-percentage> |
Initial: | normal |
Applies to: | inline boxes |
Inherited: | yes |
Percentages: | computed relative to 1em |
Computed value: | the specified keyword, a number, or a computed <length> value |
Canonical order: | per grammar |
Animation type: | discrete |
- normal
- <number>
- <length-percentage>
- <number>
- See CSS2§10.8.1.
Fill out this definition so that it fully replaces CSS2.
The fact that percentages compute to lengths is annoying. See also href="https://github.com/w3c/csswg-drafts/issues/3118">Issue 3118 and Issue 2165.
2.4. Line Sizing Containment: the line-sizing property
Name: | line-sizing |
---|---|
Value: | legacy | normal |
Initial: | legacy |
Applies to: | inline boxes |
Inherited: | yes |
Percentages: | N/A |
Computed value: | the specified keyword |
Canonical order: | per grammar |
Animation type: | discrete |
This is a rought draft of a proposal, and has not yet been approved by the CSSWG. See discussion in Issue 3199, Hyatt’s message, and dbaron’s proposal.
This property controls the method by which line boxes are sized, and thus the spacing between lines of text.
Values have the following meanings:
- legacy
-
The inline box contributes to the sizing of its line box
based on its line-height,
rather than based on its box edges,
as defined in [CSS2].
In Quirks Mode [QUIRKS],
any inline box fragment that has zero borders and padding and
that does not directly contain text or preserved white space [CSS-TEXT-3] is ignored when sizing the line box.
Note: In this model, vertical rhythm is broken any time there is a change in font metrics within a paragraph.
- normal
-
The inline box contributes to the sizing of its line box
based on its margin box,
rather than its line-height.
Half-leading is inserted inside the content box edges,
rather than overlapping the padding/border/margin areas.
However, positive half-leading is only applied to the root inline box.
Negative half-leading is applied to all inline boxes,-
reducing the size of the content box as needed.
Note: This will give consistent line spacing as long as there is some amount of leading added, such that the half-leading on the root inline is large enough to accommodate the unleaded ascent/descent of its descendants. The line box will grow, however, to accommodate content that would otherwise overflow, to avoid overlap between lines.
Should this property apply to block containers or to inline boxes? In the latter case, an individual inline could say "pay attention to me" or "don’t pay attention to me".
2.5. Leading Control: the leading-trim-over and leading-trim-under properties and leading-trim shorthand
This is a rought draft of a proposal, and is likely to change significantly as design critiques and use cases are registered. Values and property names may be added, dropped, and/or renamed, and the overall syntax or behavior may change. Do not implement (yet). The CSSWG particularly invites feedback on which font metrics need corresponding keyword values.
To ensure consistent spacing in the basic case of running text, CSS line layout introduces leading both above and below the text content of each line. In addition, the ascend and descent font metrics themselves include extra space above and below the most common glyph sizes in order to accommodate occasional characters and diacritics which ascend or descend beyond the typical bounds. This prevents subsequent lines of text from overlapping each other. However, all this extra spacing interferes with visual alignment and with control over effective (visually-apparent) spacing.
The leading-trim properties allow controlling the spacing above and below the first and last lines of a block. It allows precise control over spacing; moreover, by relying on font metrics rather than hard-coded lengths, it allows content to be resized, rewrapped, and rendered in a variety of fonts while maintaining that spacing.
A common problem is vertical centering. It’s easy to vertically center the text container to an icon, but because the visual boundaries of Latin text are the cap height and the alphabetic baseline, rather than the ascent and descent, this often doesn’t yield the intended visual effect.

To center the text visually, it’s necessary to asume the cap height and alphabetic baseline as the top and bottom edges of the text, respectively.

By using leading-trim to strip out the spacing above the cap height and below the alphabetic baseline, centering the box actually centers the text; and does so reliably, regardless of what font is used to render it.

Name: | leading-trim-over |
---|---|
Value: | normal | text | cap | ex | ideographic | ideographic-ink |
Initial: | normal |
Applies to: | block containers |
Inherited: | no |
Percentages: | N/A |
Computed value: | the specified keyword |
Canonical order: | per grammar |
Animation type: | discrete |
The leading-trim-over property trims the line-over side of the first line box in the block container to better match the box’s content edge to its text content. The property affects only the first formatted line of the block container; if there is no such line, it has no effect. Values have the following meanings:
- normal
- Half-leading is applied over the first line, just as for every other line.
- text
- Half-leading is not applied over the first line; the top of the line box is set to the text-top metric of the root inline box.
- cap
- Half-leading is not applied over the first line; the top of the line box is set to the cap-height metric of the root inline box.
- ex
- Half-leading is not applied over the first line; the top of the line box is set to the ex-height metric of the root inline box.
- ideographic
- Half-leading is not applied over the first line;
the top of the line box is set to
the ideographic top (
idtp
) metric of the root inline box. - ideographic-ink
- Half-leading is not applied over the first line;
the top of the line box is set to
the ideographic character face top (
icft
) metric of the root inline box.
Name: | leading-trim-under |
---|---|
Value: | normal | text | alphabetic | ideographic | ideographic-ink |
Initial: | normal |
Applies to: | block containers |
Inherited: | yes |
Percentages: | N/A |
Computed value: | the specified keyword |
Canonical order: | per grammar |
Animation type: | discrete |
The leading-trim-over property trims the line-over side of the first line box in the block container to better match the box’s content edge to its text content. The property affects only the first formatted line of the block container; if there is no such line, it has no effect. Values have the following meanings:
- normal
- Half-leading is applied over the first line, just as for every other line.
- text
- Half-leading is not applied over the first line; the top of the line box is set to the text-top metric of the root inline box.
- alphabetic
- Half-leading is not applied over the first line; the top of the line box is set to the alphabetic baseline metric of the root inline box.
- ideographic
- Half-leading is not applied over the first line;
the top of the line box is set to
the ideographic bottom (
ideo
) metric of the root inline box. - ideographic-ink
- Half-leading is not applied over the first line;
the top of the line box is set to
the ideographic character face top (
icfb
) metric of the root inline box.
Name: | leading-trim |
---|---|
Value: | normal | text | cap | ex | ideographic | ideographic-ink |
Initial: | normal |
Applies to: | block containers |
Inherited: | no |
Percentages: | N/A |
Computed value: | the specified keyword |
Canonical order: | per grammar |
Animation type: | discrete |
This property is a shorthand of leading-trim-over and leading-trim-under. If cap or ex is specified, leading-trim-over is set to that value and leading-trim-under is set to alphabetic; otherwise both longhands are set to the specified keyword.
3. Drawing Inline Boxes
3.1. Inline Box Heights: the inline-sizing property
Name: | inline-sizing |
---|---|
Value: | normal | stretch |
Initial: | normal |
Applies to: | inline boxes |
Inherited: | no |
Percentages: | n/a |
Computed value: | specified keyword |
Canonical order: | per grammar |
Animation type: | discrete |
This property specifies how the logical height of the content area of an inline box is measured and how it is aligned with its contents. (It has no effect on the size or position of the box’s contents.) Values have the following meanings:
- normal
- The content area of the inline box is sized and position to fit its (possibly hypothetical) text as specified in CSS2§10.6.1.
- stretch
- Once the line box has been sized, the final logical height of the inline box’s content area is calculated as the stretch fit into the line box, and it is positioned such that its margin edges coincide with the line box’s edges.
We might want to use this opportunity to more precisely define normal, rename it to match, and possibly introduce any other values that may seem necessary.
4. Initial Letters
The editors would appreciate any examples of drop initials in non-western scripts, especially Arabic and Indic scripts.
4.1. An Introduction to Initial Letters
This section is non-normative.
Large, decorative letters have been used to start new sections of text since before the invention of printing. In fact, their use predates lowercase letters entirely.
4.1.1. Drop Initial
A dropped initial (or “drop cap”) is a larger-than-usual letter at the start of a paragraph, with a baseline at least one line lower than the first baseline of the paragraph. The size of the drop initial is usually indicated by how many lines it occupies. Two- and three-line drop initials are very common.

The exact size and position of a dropped initial depends on the alignment of its glyph. Reference points on the drop cap must align precisely with reference points in the text. The alignment constraints for drop initials depend on the writing system.
In Western scripts, the top reference points are the cap height of the initial letter and of the first line of text. The bottom reference points are the alphabetic baseline of the initial letter and the baseline of the Nth line of text. Figure 2 shows a simple two-line drop cap, with the relevant reference lines marked.

In Han-derived scripts, the initial letter extends from the block-start edge of the glyphs on the first line to the block-end edge of the glyphs on the Nth line.

In certain Indic scripts, the top alignment point is the hanging baseline, and the bottom alignment point is the text-after-edge.

4.1.2. Sunken Initial Letters
Some styles of drop initials do not align with the first line of text. A sunken initial (or “sunken cap”) both sinks below the first baseline, and extends above the first line of text.

4.1.3. Raised Initial Letters
A raised initial (often called a “raised cap” or “stick-up cap”) “sinks” to the first text baseline.
Note: A proper raised initial has several advantages over simply increasing the font size of a first letter. The line spacing in the rest of the paragraph will not be altered, but text will still be excluded around large descenders. And if the size of raised initial is defined to be an integral number of lines, implicit baseline grids can be maintained.

4.2. Selecting Initial Letters
This section is non-normative.
Initial letters are typically a single letter, although they may include punctuation or a sequence of characters which are perceived by the user to be a single typographic unit. The ::first-letter pseudo-element, defined in [SELECT] and [CSS-PSEUDO-4], can be used to select the character(s) to be formatted as initial letters.
Authors who need more control over which characters are included in an initial letter, or who want to apply initial-letters formatting to replaced elements or multiple words can alternately apply the initial-letters property to the first inline-level child of a block container.
<p>This paragraph has a dropped “T”. <p><img alt="H" src="illuminated-h.svg">ere we have an illuminated “H”. <p><span>Words may also</span> be given initial letter styling at the beginning of a paragraph.
::first-letter, /* style first paragraph’s T */ img, /* style illuminated H */ span /* style phrase inside span */ { initial-letters: 2; }
Note that since ::first-letter selects punctuation before or after the first letter, these characters are included in the initial-letters when ::first-letter is used.

Should there be a way to opt out of this behavior? See Github Issue 310.
4.3. Creating Initial Letters: the initial-letters property
Name: | initial-letters |
---|---|
Value: | normal | <number> <integer> | <number> && [ drop | raise ]? |
Initial: | normal |
Applies to: | certain inline-level boxes and ::first-letter and inside ::marker boxes (see prose) |
Inherited: | no |
Percentages: | N/A |
Computed value: | the keyword normal or a number paired with an integer |
Canonical order: | per grammar |
Animation type: | by computed value type |
Renaming this property (and the others in this section) is currently under discussion.
This property specifies the size and sink for dropped, raised, and sunken initial letters as the number of lines spanned.
h2 + p::first-letter { initial-letters: 2; }
It takes the following values:
- normal
- No special initial-letters effect. Text behaves as normal.
- <number>
- This first argument defines the size of the initial letter in terms of how many lines it occupies. Values less than one are invalid.
- <integer>
- This optional second argument defines the number of lines the initial letter should sink. A value of 1 indicates a raised initial; values greater than 1 indiciate a sunken initial. Values less than one are invalid.
- raise
- Computes to an initial letter sink of 1.
- drop
- Computes to an initial letter sink equal to the initial letter size floored to the nearest positive whole number.
If the initial letter sink value is omitted, drop is assumed.
Values other than normal cause the affected box to become an initial letter box, which is an in-flow inline-level box with special layout behavior.
- initial-letters: 3
- initial-letters: 3 3
- initial-letters: 3 drop
- initial-letters: drop 3
- initial-letters: 3 3
-
Represents a dropped initial 3 lines high, 3 lines deep.
- initial-letters: 3 2
-
Represents a sunken initial 3 lines high, 2 lines deep.
- initial-letters: 3 1
- initial-letters: 3 raise
- initial-letters: raise 3
- initial-letters: 3 raise
-
Represents a raised initial 3 lines high, 1 line deep.
- initial-letters: 2.51 3
-
The size of the initial letter does not have to be an integral number of lines.
In this case only the bottom aligns.
p::first-letter { initial-letters: 3; color: red; width: 5em; text-align: right; margin-left: -5em; } p { margin-left: 5em; }

4.3.1. Applicability
To give authors more control over which characters can be styled as an initial letter and to allow the possibility of multi-character initial letters (such as for first word or first phrase styling),
the initial-letters property applies not just
to the CSS-defined ::first-letter pseudo-element,
but also to inside-positioned ::marker pseudo-elements and
inline-level boxes
that are placed at the start of the first line.
Specifically, initial-letters applies to
any inline-level box—
<span>
, <em>
, and <b>
elements
in the following example are
"first-most inline-level descendants" of the <p>
,
but the <strong>
element
is not:
<p><span><em><b>This</b> phrase</em> is styled <strong>specially</strong>.</span> …
If we apply the following rules:
em { initial-letters: 2; } b, strong { initial-letters: 3; }
The initial-letters property will take effect only on the <em>
.
The styling on <b>
is ignored,
as it has an ancestor already styled as an initial letter;
and the styling on <strong>
is ignored
because it is a second sibling.
The result might be rendered as

If initial-letters is applied to an inline-level box that is not positioned at the start of the line due to bidi reordering or which is otherwise preceded by other inline-level content, its used value is normal, and it is not formatted as an initial letter.
The effect of the initial-letters property is undefined on children of ruby base container boxes and on ruby container boxes.
Note: The initial-letters property cannot apply to any element whose float is not none or position is not static, because these values cause its display to compute to block.
4.4. Alignment of Initial Letters: the initial-letters-align property
As mentioned earlier, the alignment of initial letters depends on the script used. The initial-letters-align property can be used to specify the proper alignment.
Name: | initial-letters-align |
---|---|
Value: | border-box? [ alphabetic | ideographic | hebrew | hanging ] | border-box |
Initial: | alphabetic |
Applies to: | certain inline-level boxes and ::first-letter and inside ::marker boxes (see prose) |
Inherited: | yes |
Percentages: | N/A |
Computed value: | specified keyword(s) |
Canonical order: | per grammar |
Animation type: | discrete |
This property specifies the alignment points used to size and position an initial letter. Two sets of alignment points are necessary: the over and under alignment points of the initial letter are matched to corresponding over and under points of the surrounding text.
Values have the following meanings:
- alphabetic
- Use the alphabetic and cap-height baselines of the surrounding text to align the initial letter.
- ideographic
- Use the ideographic character face bottom and top edge baselines of the surrounding text to align the initial letter.
- hebrew
- Use the alphabetic and (as yet theoretical) hebrew hanging baseline of the surrounding text to align the initial letter.
- hanging
- Use the alphabetic and hanging baselines of the surrounding text to align the initial letter.
- border-box
- Use the initial letter box’s line-over and line-under border edges as the over and under alignment points, respectively.
Is there a proper typographic term for the hebrew “hanging” baseline?
span.initial { initial-letters: 2; initial-letters-align: ideographic; }
Except when border-box is specified, the alignment points of the initial letter are automatically determined from its contents:
- If the initial letter is an atomic inline, use its over and under content-box edges.
- Else if the initial letter contains any character from the Han, Hangul, Kana, or Yi Unicode scripts, use the ideographic character face bottom and top edge baselines.
- Else if the initial letter contains any character from the Devanagari, Bengali, and Gurmukhi Unicode scripts, use the hanging and alphabetic baselines.
- Else if the initial letter contains any character from the Hebrew Unicode scripts, use the ideographic character face bottom and top edge baselines.
- Else use the alphabetic and cap-height baselines.
What is the proper alignment for South Asian scripts that do not have the explicit hanging baseline, such as Tamil or Telugu? See GitHub issue 864
Note: The ordering of keywords in this property is fixed in case border-box is expanded to [ border-box | alphabetic | ideographic | hebrew | hanging ] to allow explicitly specifying the initial letter’s alignment points.
4.4.1. UA Default Stylesheet for initial-letters-align
In order to provide the better behavior by default, UAs must include in their default UA style sheet the following rules:
[lang]:lang(zh, ja, ko, ii) { initial-letters-align: ideographic; } [lang]:lang(iw, yi, lad, jrb) { initial-letters-align: hebrew; } [lang]:lang(hi, mr, ne, pi, kok, brx, mai, sd, sa) { initial-letters-align: hanging; } /* Script tags override language tags */ [lang]:lang('*-Latn', '*-Cyrl') { initial-letters-align: alphabetic; } [lang]:lang('*-Hani', '*-Hant', '*-Hans') { initial-letters-align: ideographic; }
This only covers the most common cross-linguistic transcription systems. Should we include any other / all script tags in the UA style sheet?
4.5. Initial Letter Layout
There are two types of initial letter boxes: those that arise from non-replaced inline boxes and those that arise from atomic inlines.
For the non-atomic inline initial letter, the box and its contents participate in the same inline formatting context as the line on which it occurs, and a lot of special rules apply to give the expected sizing and alignment.
For an atomic initial letter, however, which is either a replaced element or which establishes an independent formatting context for its contents, the sizing of the box (aside from its automatic size in the block axis) and layout of the contents within the box follows the usual rules: it is primarily the positioning of the box which is special.
4.5.1. Properties Applying to Initial Letters
All properties that apply to an inline box also apply to an inline initial letter except for vertical-align and its sub-properties, font-size, line-height, line-sizing, and inline-sizing. Additionally, all of the sizing properties and box-sizing also apply to initial letters, (see [css-sizing-3]).
All properties that apply to an atomic inline also apply to the atomic inline when styled as an initial letter, except for vertical-align and its sub-properties.
4.5.2. Margins, Borders, and Padding
Initial letters can be styled with margins, padding, and borders just like any other box. Unless initial-letters-align is border-box, its vertical alignment and sizing are not affected; however the effective exclusion area is (and corresponds to the margin area).
Reword that to handle box-sizing correctly.
When padding and borders are zero, the initial letter may be kerned; see below.
4.6. Font Sizing of Initial Letters
For an inline initial letter, the font size used for sizing the initial letter contents is calculated to fulfill its specified size (see initial-letters) as anchored by its specified alignment points (see initial-letters-align). Note that no layout is required in this calculation: it is based only on computed values and font metrics. These used font size calculations do not affect the computed font-size, and therefore have no effect on the computation of em length values, etc.
What about inheritance to descendants?
For an atomic initial letter, the used font size is the computed font size as usual.
The line height used in these calculations is the line-height of the containing block (or, in the case where a baseline grid is in use, the baseline-to-baseline spacing required by the baseline grid [CSS-LINE-GRID-1]). The contents of the lines spanned, and therefore any variation in their heights and positions, is not accounted for.

For an N-line drop initial in a Western script, the cap-height of the letter needs to be (N – 1) times the line-height, plus the cap-height of the surrounding text. Note this height is not the font size of the drop initial.
Actually calculating this font size is tricky. For an N-line drop initial, we find the drop initial font size to be:
![Font size of drop cap = ((N-1) * line-height + [cap-height of para] * [font size of paragraph])/[cap-height ratio of drop initial font]](images/InitialCapEquation.png)
Update this calculation to be a) generic across writing systems / alignment points and b) handle non-integer sizes.
4.6.1. Shaping and Glyph Selection
When initial-letters is not normal, shaping should still occur across an inline initial letter box’s boundaries. (See CSS Text 3 §7.3 Shaping Across Element Boundaries.) For example, if the first letter of the Farsi word “پس” were styled with initial-letters: 2 1, both letters would be styled in their joined forms, with initial-form “ﭘ” as the initial letter, followed by the normally-styled final-form “ﺲ”. Note that the two letters might not always graphically connect, even when shaped in their joining forms.
Are there other things we need to consider here?
4.7. Sizing the Initial Letter Box
For an inline initial letter, if the initial letter’s specified width/specified height is definite, use that value (clamped as required by the min size and max size properties, and handling box-sizing as required) for that dimension of the box.
Otherwise
it is considered to have an automatic size in that dimension
and is sized and positioned to coincide with
the smallest rectangle that would include
the bounding boxes of all its glyphs—
Should the hanging punctuation be included in the box instead (so that the box is drawn around the punctuation when it is made visible through borders/background), but rather only excluded when positioning the box (so that the initial letter remains flush, with the hanging punctuation properly hanging)? See discussion.
For atomic initial letters, sizing follows the usual rules for that type of atomic inline. However, if the box has an automatic block size (auto), then its block size is determined as for an inline initial letter with border-box alignment, and is definite.
4.7.1. Alignment Within an Initial Letter Box
By default (i.e. under automatic sizing), the content box of an inline initial letter is fitted exactly to its content, and alignment properties like text-align or align-content do not apply. However, if the box is not sized automatically:
- If the inline size is definite, text-align is honored for aligning the contents of the initial letter within its box in the inline axis (using its inline-axis bearings as usual, not the bounding box of its glyph outlines).
- If the block size is definite, align-content is honored for aligning its contents in the block axis (using its block-axis bearings, synthesizing them if needed).
4.8. Initial Letter Positioning and Spacing
4.8.1. Space Below Initial Letters
The glyph(s) of an initial letter do not always fit within the specified sink. For example, if an initial letter has a descender, it could crash into the (n+1)th line of text. This is not desirable.

Therefore all line boxes impacted by the glyph bounding boxes of an initial letter are excluded, not just those within range of the initial letter sink. Specifically, for non-atomic initial letters, the content box of the element is sized to fit:
- The specified amount of sink (i.e the distance from the top alignment point to the bottom alignment point).
- The actual ascent and descent and side bearings of all the glyphs it contains that are part of its inline formatting context, even if they leak outside their em boxes.
- The margin boxes of all the atomic inlines it contains that are part of its inline formatting context, even if they leak outside its own line-height.
The initial letter is then made an exclusion area, the same as if it were a float. See initial-letter-wrap for details.

4.8.2. Block-axis Positioning
In the block axis, the initial letter is positioned as required to satisfy its under alignment point (initial-letters-align) at its specified sink (initial-letters), i.e. it is positioned such that it would sink the number of lines specified by initial-letters’s second argument and align to the requisite under alignment point if it was assumed that its containing block held only the initial letter itself followed by an infinite sequence of plain text as the direct contents of its root inline box.

Its position is anchored with respect to the line on which it occurs.
4.8.3. Inline Positioning and Kerning
In the inline axis, the position of the inline letter is given by matching its inline-start margin edge with the inline-start edge of the line box.
However, if the initial letter is a non-atomic inline with an automatic inline size and zero padding and borders, it is negatively offset by the distance from the start edge of its content box to the point in the content that would have been placed at the start edge of the containing block if it were not an initial letter (i.e. the distance between its glyph bounding box and its start side bearing).
4.9. Initial Letter Wrapping: the initial-letters-wrap property
Note: initial-letters-wrap is at risk.
Name: | initial-letters-wrap |
---|---|
Value: | none | first | all | grid | <length-percentage> |
Initial: | none |
Applies to: | certain inline-level boxes and ::first-letter and inside ::marker boxes (see prose) |
Inherited: | yes |
Percentages: | relative to logical width of (last fragment of) initial letter |
Computed value: | specified keyword or computed <length-percentage> value |
Canonical order: | per grammar |
Animation type: | by computed value type |
This property specifies whether lines impacted by an initial letter are shortened to fit the rectangular shape of the initial letter box or follow the contour of its end-edge glyph outline.
- none
- No contour-fitting is performed: each impacted line is aligned flush to the end margin edge of the initial letter.
- first
-
Behaves as none if the first typographic character unit after the initial letter belongs to Unicode General Category Zs.
Otherwise behaves as for all on the first line of the block containing the initial letter
and as none on the rest.
This example shows why contour-fitting the first line is necessary, and why it is dropped when the initial letter is followed by a space:
In the top paragraph, the initial letter "A" has a word space after it: the gap between the top of the "A" and the next letter provides the necessary word separation. In the next paragraph, the initial letter "A" is part of the first word, and leaving a gap between the top of the "A" and the next letter would create a jarring visual break within the word. In this case, the first line of text should be kerned into the initial letter’s area, as shown in the bottom paragraph. Do we need an unconditional first? (I.e. Should we rename this value to auto and add a first value that does not check for spaces?) See GitHub issue 410
- all
-
For each line of text impacted by the initial letter,
the line box adjacent to the initial letter starts
at the start-most point that touches the ink of the initial letter,
plus the amount of the initial letter’s end-side border+padding+margin.
If the value of shape-outside is not none, shape-outside is used instead of the glyph outline.
Note: This value is at-risk.
- grid
-
This value is the same as none,
except that the exclusion area of the impacted lines
is increased as necessary for its end-edge to land on the character grid,
i.e. to be a multiple of (1ic + letter-spacing)
as computed on the containing block.
The justify-self property can then be used to align
the initial letter box within the exclusion area.
Diagram of Japanese initial letter in vertical writing mode Note: In this example, the exclusion area for the drop initial is larger than its glyph in order to preserve inline-axis alignment.
Note: This value is also at-risk.
- <length>
- <percentage>
-
This value behaves the same as first except that the adjustment to the first line is given explicitly
instead of being inferred from the glyph shape.
This really needs font-relative lengths to be relative to the used size.
Note: This value exists because it is easier to implement. Authors are encouraged to use the first value and to set margins to control spacing, and to use this as a fallback for glyph detection if necessary.
In the following example, UAs that support first will use the glyph outline plus the specified margin in order to place the first line, whereas UAs that only support <length> or <percentage> values will pull in the first line by 40% of the initial letter’s width (and then add the margin to that point).h1 + p:first-letter { initial-letters: 3; /* 3-line drop-cap */ initial-letters-wrap: first; margin-right: 0.1em; } @supports (not (initial-letters-wrap: first)) { /* Classes auto-generated on paragraphs to match first letter. */ p.A:first-letter { initial-letters-wrap: -40%; /* Start of glyph outline, assuming correct font. */ } }
These values and related annoyance is likely unnecessary if someone submits a patch to Blink to support first.
Edit figure to show how auto behaves in varying contexts
p::first-letter { initial-letters: 3; initial-letters-wrap: none; }

p::first-letter { initial-letters: 3; initial-letters-wrap: all; }
Text follows shape of initial letter. Each line box should just touch the ink of the letter, with some offset (represented by the shaded box).
p::first-letter { initial-letters: 3; initial-letters-wrap: first; }
Only the first line is moved up against the ink of the initial letter.
4.10. Line Layout
An initial letter box is considered in-flow in its block formatting context, and is part of the contents of the line box in which it originates. Aside from vertical alignment, its interaction with the rest of the contents of the line is as normal, except in a few specific circumstances…
4.10.1. Inline Flow Layout: Alignment and Justification
For a raised initial no special consideration is given for alignment and justification: it is treated similar to any other inline-level content.
However, for a sunken initial its inline-start edge is anchored to the inline-start edge of the line box (after indentation) and text alignment affects the remaining content of the line in the remaining space, without moving the initial letter box itself.
Note: The CSSWG was not aware of any reasonable use cases for mixing non-start text alignment with dropped initial letters, and this was the most sensible behavior proposed. This behavior may be reconsidered if use cases require otherwise.
In addition, to ensure consistent alignment of all the impacted lines, any letter-spacing or justification opportunity that would normally be introduced by the juxtaposition of the contents of a sunken initial and the subsequent contents of the line is suppressed. (Note that this does not affect word-spacing or the justification opportunity introduced by a word separator because that space is provided by the typographic character unit alone and not by its juxtaposition with an adjacent character.)
4.10.2. Edge Effects: Indentation and Hanging Punctuation
text-indent and hanging-punctuation apply to the first line of text as normal in the presence of initial letters. Lines affected by the exclusion are shortened, as in the presence of floats, and are affected the same way.

The interaction of initial-letters and hanging-punctuation is under discussion.
4.10.3. Ancestor Inlines
If the initial letter box is contained by inline box ancestors, the boundaries of those inline boxes are drawn to exclude the initial letter box, as if it were outside their startmost margin edge. This is a purely geometric operation: it does not affect e.g. property inheritance or the effective letter-spacing between the initial letter box and subsequent content.
4.10.4. Multi-line Initial Letters
If an initial letter is too long to fit on one line, it wraps (according to the usual text-wrapping rules), each line filled and formatted exactly as if it were the first line and the initial letter too long to fit any subsequent normal text. Any normal text after the initial letter starts on its last line, affected exactly as if that line were the first line.
4.11. Clearing Initial Letters
4.11.1. Raised and sunken caps
The margin box of an initial letter contributes to the size of its containing element. Initial letters that extend above the first line of text, known as “raised caps” or “sunken caps,” do not extend up into previous elements. Since the content box for an initial letter includes all glyph ink, this also means that accents or other ink above the cap height of an initial letter will not impinge on previous elements.

initial-letters: 3 1
) on right;
note that the position of the “C” is the same in both cases,
but on the right all text is moved down relative to the initial letter. Handle glyph ink above cap height of font. Proposal: Make it an exclusion area for line boxes and border boxes. Include margin specified on initial-letters as part of exclusion area in order to control spacing.
Draw a box model diagram here. Does the margin of the initial letter collapse with its container?
4.11.2. Short paragraphs with initial letters
A paragraph with an initial letter can have fewer lines of text
than the initial letter occupies.
In this case, the initial letter’s top alignment is still honored,
and its exclusion area continues into any subsequent blocks.
This forces the subsequent inline-level content to wrap around the initial letter—

If the subsequent block starts with an initial letter, establishes an independent formatting context, or specifies clear in the initial letter’s containing block’s start direction, then it must clear the previous block’s initial letter.

4.11.3. Interaction with floats
Initial letters are not floats: they are in-flow inline-level content that belongs to a line box. Therefore:
- The clear property does not care about initial letters: it neither applies to initial letters nor clears them when applied to nearby floats.
- Like line boxes or floats, initial letter boxes must not overlap the margin boxes of any floats participating in the same block formatting context. An overlapping initial letter box is shifted inward or downward until either it fits without overlapping or there are no more floats present.
- If a line box’s start edge shifts or moves down to clear a float, an initial letter originating in it moves with it; likewise if an initial letter shifts inward or moves downward to clear a float, its originating line box and subsequent line boxes shorten and/or move accordingly.
-
If an inline-start float
originates in the first line of content
adjacent to an initial letter,
then it moves past the initial letter towards the containing block edge,
exactly as if the initial letter were any other inline-level content.
However, if such a float originates in subsequent lines of content adjacent to a (sunk) initial letter, then that float must clear the initial letter.

See CSS2§9.5 for more information about the layout of floats and adjacent content. [CSS2]
Whether an inline-end float originating in subsequent lines must clear the initial letter (as inline-start floats do) is still under discussion. There is no aesthetic reason to require it; however it’s yet unclear how the underlying layout model would distinguish between the two cases.
4.11.4. Interaction with Fragmentation (Pagination)
Since a single glyph cannot be fragmented across pages (or columns or other fragmentation containers), an initial letter is considered monolithic [css-break-3] for the purpose of block-axis fragmentation (breaking across pages, columns, regions, etc.). Additionally, breaks between the in-flow lines alongside an initial letter box are avoided, much as breaks between line boxes affected be widows and orphans are avoided. However, if there is a forced break alongside the initial letter box, then it takes precedence; but has no effect on the initial letter box itself.
As with other monolithic objects, if an initial letter box occurs at the top of a fragmentation container and that fragmentation container is too short to contain it, it may be either truncated or sliced. Adjacent content, however, must be fragmented according to its own rules, not truncated or sliced along with the initial letter.
Appendix A: Synthesizing Alignment Metrics
A.1: Synthesizing Baselines (and Other Font Metrics) for Text
Some fonts might not contain the metrics information necessary to align text properly as described in this module. User agents may use the following strategies in the absence of a required metric:
- Measure the font
-
Metrics may be derived from the glyph shapes.
For example,
- The center of the minus sign (U+2212) can be taken as the mathematical baseline.
-
The amount by which the lowercase “o”
descends below the alphabetic baseline
can be subtracted from its highest point
to measure the x-height.
Measuring the x height. - The amount by which the uppercase “O” descends below the alphabetic baseline can be subtracted from its highest point to measure the cap-height.
- The bounding box of 永 (U+6C38) can be used to find the ideographic character face edges.
- The top edge of the center of the Hebrew maqaf (U+05B3 “־”) can be taken as the Hebrew hanging baseline.
-
The top edge of the center of the letter Ka
can be taken as the hanging baseline.
Which Ka is used should depend on the content language:
Language Script Letter Devanagari क U+0915 KA Bengali ক U+0995 Gurmukhi ਕ U+0A15 Tibetan ཀ U+0F40 The hanging baseline is at the top edge of the character ink. - Issue: Add more notes here?
- Use a heuristic for the script
- Issue: What does this mean?
- Use fallback values
-
The following fallback values
- x-height: .5em;
- cap-height: .66em;
- hanging baseline: .6em;
- Hebrew hanging baseline: ???
A.2: Synthesizing Baselines for Replaced Content
Copy over text from CSS Writing Modes and expand for additional baseline values.
Note: Authors can use margins (positive or negative) to adjust the alignment of replaced content within a line.
In this example, the author is using a set of images to display characters that don’t exist.img[src^="/text/"] { height: 1em; /* Size to match adjacent text */ margin-bottom: -0.2em; /* Baseline at 20% above bottom */ } ... <p>This is some text with words written in an unencoded script: <img src="/text/ch3439.png" alt="..."> <img src="/text/ch3440.png" alt="..."> <img src="/text/ch3442.png" alt="...">
Note: A future level of CSS may include a way of specifying a full baseline table for replaced elements. (This will probably look like a baseline-table property that accepts ''[<baseline-keyword> <percentage>]+''.)
Changes
Changes since the 8 August 2018 Working Draft include:
- Added line-sizing property to control how inter-line spacing is calculated. (Issue 3199)
Changes since the 24 May 2016 Working Draft include:
- Sketched out property to control the logical height of inline boxes. (Issue 1974)
- Better defined handling of initial letters that are descendants of other inline boxes and clarified applicability in the presence of ::marker, bidi reordering, and other complications. (Issue 2184, Issue 2705)
- Defined interaction of initial letters and text-align, letter-spacing, and justification. (Issue 884)
- Renamed initial-letter to initial-letters. (Issue 862)
- Better defined interaction of initial letters and floats. (Issue 360, Issue 689)
- Improved recommended default UA style sheet rules for initial letters.
- Changed applicability of properties to initial letters from explicit list to reference to properties applying to inline boxes (with a few exceptions). (Issue 2700)
- Defined sizing properties to apply to initial letters. (Issue 863)
- Defined shape-outside to apply to initial letters with initial-letter-wrap: all. (Issue 885)
- Specified that Arabic shaping applies between an initial letter and subsequent text. (Issue 2399)
- Defined interaction of initial letters and fragmentation. (Issue 2404)
- Fixed math errors in definition of initial-letter-wrap: grid. (Issue 947)
Acknowledgments
Special thanks goes to the initial authors, Eric A. Meyer and Michel Suignard.
In additions to the authors, this specification would not have been possible without the help from:
David Baron, David M Brown, Oriol Brufau, John Daggett, Stephen Deach, Sylvain Galineau, David Hyatt, Myles Maxfield, Shinyu Murakami, Jan Nicklas, Tess O’Connor, Sujal Parikh, Florian Rivoal, Alan Stearns, Weston Thayer, Bobby Tung, Chris Wilson, Grzegorz Zygmunt.