This CSS module defines a two-dimensional grid-based layout system, optimized for user interface design. In the grid layout model, the children of a grid container can be positioned into arbitrary slots in a flexible or fixed predefined layout grid.
CSS is a language for describing the rendering of structured documents
(such as HTML and XML)
on screen, on paper, in speech, etc.
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current W3C publications and the latest revision of this technical report
can be found in the W3C technical reports
index at http://www.w3.org/TR/.
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obsoleted by other documents at any time. It is inappropriate to cite this
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Grid layout contains features targeted at web application authors.
The grid can be used to achieve many different layouts.
It excels at dividing up space for major regions of an application,
or defining the relationship in terms of size, position, and layer
between parts of a control built from HTML primitives.
Like tables,
grid layout enables an author to align elements into columns and rows,
but unlike tables,
grid layout doesn’t have content structure,
and thus enables a wide variety of layouts not possible with tables.
For example, the children of a grid container can position themselves
such that they overlap and layer similar to positioned elements.
In addition, the absence of content structure in grid layout helps to manage changes to layout
by using fluid and source order independent layout techniques.
By combining media queries with the CSS properties that control layout of the grid container and its children,
authors can adapt their layout to changes in device form factors, orientation, and available space,
without needing to alter the semantic nature of their content.
1.1.
Background and Motivation
As websites evolved from simple documents into complex, interactive applications,
tools for document layout, e.g. floats,
were not necessarily well suited for application layout.
By using a combination of tables, JavaScript, or careful measurements on floated elements,
authors discovered workarounds to achieve desired layouts.
Layouts that adapted to the available space were often brittle
and resulted in counter-intuitive behavior as space became constrained.
As an alternative, authors of many web applications opted for a fixed layout
that cannot take advantage of changes in the available rendering space on a screen.
The capabilities of grid layout address these problems.
It provides a mechanism for authors to divide available space for layout into columns and rows
using a set of predictable sizing behaviors.
Authors can then precisely position and size the building block elements of their application
by into grid areas defined by these columns and rows.
Figure 1 illustrates a basic layout which can be achieved with grid layout.
1.2.
Adapting Layouts to Available Space
Grid layout can be used to intelligently reflow elements within a webpage.
Figure 2 represents a game with five major areas in the layout:
the game title, stats area, game board, score area, and control area.
The author’s intent is to divide the space for the game such that:
The stats area always appears immediately under the game title.
The game board appears to the right of the stats and title.
The top of the game title and the game board should always align.
The bottom of the game board and the stats area align when the game has reached its minimum height,
but otherwise the game board will stretch to take advantage of all the screen real-estate available to it.
The score area should align into the column created by the game and stats area,
while the controls are centered under the board.
As an alternative to using script to control the absolute position, width, and height of all elements,
the author can use grid layout,
as shown in Figure 3.
The following example shows how an author might achieve all the sizing, placement, and alignment rules declaratively.
Note that there are multiple ways to specify the structure of the grid
and to position and size grid items,
each optimized for different scenarios.
This example illustrates one that an author may use to define the position and space for each grid item
using the grid-template-rows and grid-template-columns properties on the grid container,
and the grid-row and grid-column properties on each grid item.
#grid {
display: grid;
/* Two columns: the first sized to content, the second receives
* the remaining space, but is never smaller than the minimum
* size of the board or the game controls, which occupy this
* column. */
grid-template-columns: auto minmax(min-content, 1fr);
/* Three rows: the first and last sized to content, the middle
* row receives the remaining space, but is never smaller than
* the minimum height of the board or stats areas. */
grid-template-rows: auto minmax(min-content, 1fr) auto
}
/* Each part of the game is positioned between grid lines by
* referencing the starting grid line and then specifying, if more
* than one, the number of rows or columns spanned to determine
* the ending grid line, which establishes bounds for the part. */
#title { grid-column: 1; grid-row: 1 }
#score { grid-column: 1; grid-row: 3 }
#stats { grid-column: 1; grid-row: 2; justify-self: start }
#board { grid-column: 2; grid-row: 1 / span 2; }
#controls { grid-column: 2; grid-row: 3; align-self: center }
Continuing the prior example,
the author also wants the game to adapt to the space available on traditional computer monitors, handheld devices, or tablet computers.
Also, the game should optimize the placement of the components when viewed either in landscape or portrait orientation (Figures 4 and 5).
By combining grid layout with media queries,
the author is able to use the same semantic markup,
but rearrange the layout of elements independent of their source order,
to achieve the desired layout in both orientations.
The following example leverages grid layout’s ability to name the space which will be occupied by a grid item.
This allows the author to avoid rewriting rules for grid items
as the grid’s definition changes.
<style type="text/css">
@media (orientation: portrait) {
#grid {
display: grid;
/* The rows, columns and areas of the grid are defined visually
* using the grid-template-areas property. Each string is a row, and
* each word an area. The number of words in a string
* determines the number of columns. Note the number of words
* in each string must be identical. */
grid-template-areas: "title stats"
"score stats"
"board board"
"ctrls ctrls";
/* Columns and rows created with the template property can be
* assigned a sizing function with the grid-template-columns
* and grid-template-rows properties. */
grid-template-columns: auto minmax(min-content, 1fr);
grid-template-rows: auto auto minmax(min-content, 1fr) auto
}
}
@media (orientation: landscape) {
#grid {
display: grid;
/* Again the template property defines areas of the same name,
* but this time positioned differently to better suit a
* landscape orientation. */
grid-template-areas: "title board"
"stats board"
"score ctrls";
grid-template-columns: auto minmax(min-content, 1fr);
grid-template-rows: auto minmax(min-content, 1fr) auto
}
}
/* The grid-area property places a grid item into a named
* region (area) of the grid. */
#title { grid-area: title }
#score { grid-area: score }
#stats { grid-area: stats }
#board { grid-area: board }
#controls { grid-area: ctrls }
</style>
<div id="grid">
<div id="title">Game Title</div>
<div id="score">Score</div>
<div id="stats">Stats</div>
<div id="board">Board</div>
<div id="controls">Controls</div>
</div>
1.4.
Grid Layering of Elements
In the example shown in Figure 6,
the author is creating a custom slider control.
The control has six parts.
The lower and upper labels align to the left and right edges of the control.
The track of the slider spans the area between the labels.
The lower and upper fill parts touch beneath the thumb,
and the thumb is a fixed width and height that can be moved along the track
by updating the two flex-sized columns.
Prior to the introduction of grid layout,
the author would have likely used absolute positioning to control the top and left coordinates,
along with the width and height of each HTML element that comprises the control.
By leveraging grid layout,
the author can instead limit script usage to handling mouse events on the thumb,
which snaps to various positions along the track
as the grid-template-columns property of the grid container is updated.
<style type="text/css">
#grid {
display: grid;
/* The grid-template-columns and rows properties also support
* naming grid lines which can then be used to position grid
* items. The line names are assigned on either side of a column
* or row sizing function where the line would logically exist. */
grid-template-columns:
(start) auto
(track-start) 0.5fr
(thumb-start) auto
(fill-split) auto
(thumb-end) 0.5fr
(track-end) auto
(end);
}
/* The grid-placement properties accept named lines. Below the
* lines are referred to by name. Beyond any
* semantic advantage, the names also allow the author to avoid
* renumbering the grid-column-start and grid-row-start properties of the
* grid items. This is similar to the concept demonstrated in the
* prior example with the grid-template-areas property during orientation
* changes, but grid lines can also work with layered grid items
* that have overlapping areas of different shapes like the thumb
* and track parts in this example. */
#lower-label { grid-column-start: start }
#track { grid-column: track-start / track-end; align-self: center }
#upper-label { grid-column-end: end; }
/* Fill parts are drawn above the track so set z-index to 5. */
#lower-fill { grid-column: track-start / fill-split;
align-self: end;
z-index: 5 }
#upper-fill { grid-column: fill-split / track-end;
align-self: start;
z-index: 5 }
/* Thumb is the topmost part; assign it the highest z-index value. */
#thumb { grid-column: thumb-start / thumb-end; z-index: 10 }
</style>
<div id="grid">
<div id="lower-label">Lower Label</div>
<div id="upper-label">Upper Label</div>
<div id="track">Track</div>
<div id="lower-fill">Lower Fill</div>
<div id="upper-fill">Upper Fill</div>
<div id="thumb">Thumb</div>
</div>
2.
Grid Layout Concepts and Terminology
In grid layout,
the content of a grid container is laid out
by positioning and aligning it into a grid.
The grid is an intersecting set of horizontal and vertical grid lines
that divides the grid container’s space into grid areas,
into which grid items (representing the grid container’s content) can be placed.
There are two sets of grid lines:
one set defining columns
that run along the block axis (the column axis),
and an orthogonal set defining rows
along the inline axis (the row axis).
[CSS3-WRITING-MODES]
2.1.
Grid Tracks and Cells
Grid track is a generic term for a grid column or grid row—in
other words, it is the space between two adjacent grid lines.
Each grid track is assigned a sizing function,
which controls how wide or tall the column or row may grow,
and thus how far apart its bounding grid lines are.
A grid cell is the similar term for the full grid—it
is the space between two adjacent row and two adjacent column grid lines.
It is the smallest unit of the grid that can be referenced when positioning grid items.
In the following example there are two columns and three rows.
The first column is fixed at 150px.
The second column uses flexible sizing, which is a function of the unassigned space in the Grid,
and thus will vary as the width of the grid container changes.
If the used width of the grid container is 200px, then the second column 50px wide.
If the used width of the grid container is 100px, then the second column is 0px
and any content positioned in the column will overflow the grid container.
Grid lines are the horizontal and vertical dividing lines of the grid.
A grid line exists on either side of a column or row.
They can be referred to by numerical index,
or by an author-specified name.
A grid item references the grid lines to determine its position within the grid
using the grid-placement properties.
The following two examples create three column grid lines and four row grid lines.
The first example demonstrates how an author would position a grid item using grid line numbers.
The second example uses explicitly named grid lines.
<style type="text/css">
/* using the template syntax */
#grid {
display: grid;
grid-template-areas: ". a"
"b a"
". a";
grid-template-columns: 150px 1fr;
grid-template-rows: 50px 1fr 50px
}
#item1 { grid-area: a }
#item2 { grid-area: b }
#item3 { grid-area: b }
/* Align items 2 and 3 at different points in the Grid Area "b". */
/* By default, Grid Items are stretched to fit their Grid Area */
/* and these items would layer one over the other. */
#item2 { align-self: start }
#item3 { justify-self: end; align-self: end }
</style>
A grid item’s grid area forms the containing block into which it is laid out.
Percentage lengths specified on a grid item resolve against this containing block.
Percentages specified for margin-top, padding-top, margin-bottom, and padding-bottom on a grid item
resolve against the height of its containing block,
rather than the width (as for blocks).
Grid items placed into the same grid area do not directly affect each other’s layout.
Indirectly, a grid item can affect the position of a grid line in a column or row that uses a contents-based relative size,
which in turn can affect the position or size of another grid item.
This value causes an element to generate a block-level grid container box.
inline-grid
This value causes an element to generate an inline-level grid container box.
A grid container establishes a new grid formatting context for its contents.
This is the same as establishing a block formatting context,
except that grid layout is used instead of block layout:
floats do not intrude into the grid container,
and the grid container’s margins do not collapse with the margins of its contents.
Grid containers form a containing block for their contents
exactly like block containers do. [CSS21]
The overflow property applies to grid containers.
Grid containers are not block containers,
and so some properties that were designed with the assumption of block layout
don’t apply in the context of grid layout.
In particular:
all of the column-* properties in the Multicol module have no effect on a grid container.
float and clear have no effect on a grid item.
(However, the float property still affects the computed value of display on children of a grid container,
as this occurs beforegrid items are determined.)
the ::first-line and ::first-letter pseudo-elements do not apply to grid containers,
and grid containers do not contribute a first formatted line or first letter to their ancestors.
If an element’s specified display is inline-grid
and the element is floated or absolutely positioned,
the computed value of display is grid.
The table in CSS 2.1 Chapter 9.7 is thus amended
to contain an additional row,
with inline-grid in the "Specified Value" column
and grid in the "Computed Value" column.
3.2.
Sizing Grid Containers
A grid container is sized
using the rules of the formatting context in which it participates.
As a block-level box in a block formatting context,
it is sized like any other block-level box that establishes a formatting context,
with an auto inline size calculated as for in-flow block boxes.
As an inline-level box in an inline formatting context,
it is sized as an atomic inline-level box (such as an inline-block).
In both inline and block formatting contexts,
the grid container’s auto block size is its max-content size.
The block layout spec should define this?
The max-content size of a grid container is
the sum of the grid container’s track sizes in the appropriate axis,
when the grid is sized under a max-content constraint.
The min-content size of a grid container is
the sum of the grid container’s track sizes in the appropriate axis,
when the grid is sized under a min-content constraint.
See [CSS3-SIZING] for a definition of the terms in this section.
4.
Grid Items
The contents of a grid container consists of zero or more grid items:
each child of a grid container
becomes a grid item,
and each contiguous run of text that is directly contained inside a grid container
is wrapped in an anonymous grid item.
However, an anonymous grid item that contains only
white space
is not rendered, as if it were display:none.
Future display types may generate anonymous containers (e.g. ruby) or otherwise mangle the box tree (e.g. run-ins).
It is intended that grid item determination run after these operations.
A grid item establishes a new formatting context for its contents.
The type of this formatting context is determined by its display value, as usual.
The computed display of a grid item
is determined by applying the table in
CSS 2.1 Chapter 9.7.
However, grid items are grid-level boxes, not block-level boxes:
they participate in their container’s grid formatting context,
not in a block formatting context.
A grid item is sized within the containing block defined by its grid area
similarly to an equivalent block-level box in an equivalently-sized containing block,
except that auto margins and the box alignment properties
have special effects. (See §10
Alignment.)
The auto value of min-width and min-height
behaves on grid items in the relevant axis
analogously to its behavior on flex items in the main axis.
See [CSS3-FLEXBOX].
ISSUE: Review implications of intrinsic ratio and Grid’s 2D nature.
4.1.
Collapsed Grid Items: the visibility property
The static position[CSS21]
of an absolutely-positioned child of a grid container
is determined as if it were the sole grid item
in a grid area
whose edges coincide with the padding edges of the grid container.
Note: Note that this position is affected by the values of justify-self and align-self on the child,
and that, as in most other layout models,
the absolutely-positioned child has no effect on the size of the containing block
or layout of its contents.
Grid items can overlap when they are positioned into intersecting grid areas,
or even when positioned in non-intersecting areas because of negative margins or positioning.
The painting order of grid items is exactly the same as inline blocks [CSS21],
except that order-modified document order is used in place of raw document order,
and z-index values other than auto create a stacking context even if position is static.
Thus the z-index property can easily be used to control the z-axis order of grid items.
Note: Descendants that are positioned outside a grid item still participate in any stacking context established by the grid item.
The following diagram shows several overlapping grid items,
with a combination of implicit source order
and explicit z-index
used to control their stacking order.
refer to corresponding dimension of the content area
Media:
visual
Computed value:
As specified, except for auto (see prose), with lengths made absolute
Animatable:
no
These properties specify,
as a space-separated track list,
the line names and track sizing functions of the grid.
Each track sizing function can be specified as a length,
a percentage of the grid container’s size,
a measurement of the contents occupying the column or row,
or a fraction of the free space in the grid.
It can also be specified as a range using the minmax() notation,
which can combine any of the previously mentioned mechanisms
to specify separate min
and max track sizing functions for the column or row.
The grid-template-columns property specifies the track list for the grid’s columns,
while grid-template-rows specifies the track list for the grid’s rows.
The none value indicates that there is no explicit grid;
any rows/columns will be implicitly generated,
and their size will be determined by the grid-auto-rows and grid-auto-columns properties.
The subgrid value indicates that the grid will align to its parent grid in that axis.
Rather than specifying the sizes of rows/columns explicitly,
they’ll be taken from the parent grid’s definition.
The syntax of a track list is:
A non-negative dimension with the unit fr specifying the track’s flex factor.
Each <flex>-sized track takes a share of the remaining space in proportion to its flex factor.
See Flexible Lengths for more details.
When appearing outside a minmax() notation,
implies an automatic minimum (i.e. ''minmax(auto, <flex>)'').
Defines a size range
greater than or equal to min
and less than or equal to max.
If max < min,
then max is ignored and minmax(min,max) is treated as min.
As a maximum, a <flex> value sets the track’s flex factor.
As a minimum, it is treated as zero
(or min-content, if the grid container is sized under a min-content constraint).
A distance from the previous line equal to half the free space
(the width of the grid container, minus the width of the non-flexible grid tracks).
A distance from the previous line equal to the maximum size of any grid items
belonging to the column between these two lines.
A distance from the previous line at least as large as the largest minimum size of any grid items
belonging to the column between these two lines,
but no larger than the other half of the free space.
If the non-flexible sizes
(100px, max-content, and min-content)
sum to larger than the grid container’s width,
the final grid line will be a distance equal to their sum away from the start edge of the grid container
(the 1fr sizes both resolve to 0).
If the sum is less than the grid container’s width,
the final grid line will be exactly at the end edge of the grid container.
This is true in general whenever there’s at least one <flex> value among the grid track sizes.
Additional examples of valid grid track definitions:
5.1.2.
Repeating Rows and Columns: the repeat() notation
The repeat() notation represents a repeated fragment of the track list,
allowing a large number of columns or rows that exhibit a recurring pattern
to be written in a more compact form.
The syntax of the repeat() notation is:
The first argument specifies the number of repetitions.
The second argument is a track list,
which is repeated that number of times.
The repeat() notation cannot be nested;
doing so makes the declaration invalid.
If the number of repetitions is auto
and the grid container has a definite size in the relevant axis,
then the number of repetitions is the largest possible integer
that does not cause the grid to overflow its grid container
(treating all tracks as their max track sizing function if that is definite or as zero otherwise).
Otherwise, the track list repeats only once.
A <track-list> with more than one autorepeat() function is invalid.
This example shows two equivalent ways of writing the same grid definition.
Both ways produce a grid with a single row and four "main" columns, each 250px wide,
surrounded by 10px "gutter" columns.
If the repeat() function ends up placing two <line-names> adjacent to each other,
the name lists are merged.
For example, repeat(2, (a) 1fr (b)) is equivalent to (a) 1fr (b a) 1fr (b).
Note: It is expected that a future level of this specification will define a value to be inserted between the repetitions,
similar to the argument of the Array#join method in JavaScript.
Issue: There’s no ability currently to fill the grid with columns based on number of items.
See thread.
(This might be better handled in Flexbox.)
5.1.3.
Flexible Lengths: the fr unit
A flexible length or <flex> is a dimension with the fr unit,
which represents a fraction of the free space in the grid container.
The distribution of free space occurs after all non-flexible track sizing functions have reached their maximum.
The total size of such rows or columns is subtracted from the available space, yielding the free space,
which is then divided among the flex-sized rows and columns in proportion to their flex factor.
Note: Flexible lengths in a track list work similarly to flexible lengths with a zero base size in [CSS3-FLEXBOX].
Each column or row’s share of the free space can be computed as the column or row’s
<flex> * <free space> / <sum of all flex factors.
For the purpose of this calculation,
a flexible length in the min position of a minmax() function is treated as 0 (an inflexible length).
When the available space is infinite
(which happens when the grid container’s width or height is indefinite),
flex-sized grid tracks are sized to their contents while retaining their respective proportions.
The used size of each flex-sized grid track is computed by
determining the max-content size of each flex-sized grid track
and dividing that size by the respective flex factor
to determine a “hypothetical 1fr size”.
The maximum of those is used as the resolved 1fr length (the flex fraction),
which is then multiplied by each grid track’s flex factor to determine its final size.
The grid-placement properties of the subgrid’s grid items
are scoped to the lines covered by the subgrid.
E.g., numeric indices count starting from the first line of the subgrid
rather than the first line of the parent grid.
The subgrid’s own grid items participate in the sizing of its parent grid and are aligned to it.
In this process, the sum of the item’s margin, padding, and borders are applied as an extra layer of margin to the items at those edges.
For example, if we have a 3×3 grid with the following tracks:
#parent-grid { grid-template-columns: 300px auto 300px; }
If a subgrid covers the last two tracks, its first two columns correspond to the parent grid’s last two columns,
and any items positioned into those tracks participate in sizing the parent grid.
Specifically, an item positioned in the first track of the subgrid
influences the auto-sizing of the parent grid’s middle track.
If the subgrid has margins/borders/padding,
the the size of those margins/borders/padding also influence sizing.
For example, if the subgrid has 100px padding:
#subgrid { padding: 100px; }
Then when the parent grid auto-sizes its second track,
it will be at least 100px wider than any items in the subgrid’s first track,
and any items in the subgrid’s second track will be sized to fit a slot 200px wide (instead of 300px wide).
However, any overflow tracks
(i.e. those outside the explicit grid when the subgrid has a definite grid span)
do not correspond to any tracks in the parent grid;
they effectively extend in a third dimension.
For example, if a parent grid has adjacent tracks A, B, and C,
and a span 1 subgrid with an extra implicit grid track is placed in track B,
the items in that implicit grid track are not considered part of track B.
The subgrid is always stretched;
the align-self/justify-self properties on it are ignored.
Any specified width/height constraints are also ignored.
Layoutwise, the subgrid’s explicit grid is always aligned with the corresponding section of the parent grid;
the align-content/justify-content properties on it are ignored.
However, overflow does apply,
so the contents of the subgrid can be scrolled aside.
(Note: the act of scrolling does not affect layout.)
Explicit named lines can also be specified together with the subgrid keyword;
these names apply (within the subgrid) to the corresponding lines of the parent grid.
If the subgrid has an explicit grid span,
any names specified for lines beyond the span are ignored.
For example, if the subgrid above were specified with 5 names:
Items within the subgrid could be positioned using the first four line names;
the last name would be ignored (as if it didn’t exist),
since the subgrid only covers four lines.
If the subgrid has an explicit grid position as well as an explicit grid span,
it also automatically receives the line names specified for its parent grid.
(In such cases the author can rely on the names specified in the parent grid,
and does not need to duplicate those names in each subgrid declaration.)
Note: In general, resolved values are the computed values,
except for a small list of legacy 2.1 properties.
However, compatibility with early implementations of this module
requires us to define grid-template-rows and grid-template-columns as returning used values.
Authors are recommended to use the
.rawComputedStyle and .usedStyle attributes
instead of getComputedStyle().
This property specifies named grid areas,
which are not associated with any particular grid item,
but can be referenced from the grid-placement properties.
The syntax of the grid-template-areas property also provides a visualization
of the structure of the grid,
making the overall layout of the grid container easier to understand.
Values have the following meanings:
A row is created for every separate string listed for the grid-template-areas property,
and a column is created for each cell in the string,
when parsed as follows:
Tokenize the string into a list of the following tokens,
using longest-match semantics:
A sequence of name code points,
representing a named cell token
with a name consisting of its code points.
A "." (U+002E FULL STOP),
representing a null cell token.
A sequence of whitespace,
representing nothing
(do not produce a token).
A sequence of any other characters,
representing a trash token.
Note: These rules can produce cell names that do not match the <ident> syntax,
such as "1st 2nd 3rd",
which requires escaping when referencing those areas by name in other properties,
like grid-row: \31st; to reference the area named 1st.
A trash token is a syntax error,
and makes the declaration invalid.
All strings must have the same number of columns,
or else the declaration is invalid.
If a named grid area spans multiple grid cells,
but those cells do not form a single filled-in rectangle,
the declaration is invalid.
Note: Non-rectangular or disconnected regions may be permitted in a future version of this module.
In this example, the grid-template-areas property is used to create a page layout
where areas are defined for header content (head),
navigational content (nav),
footer content (foot),
and main content (main).
Accordingly, the template creates three rows and two columns,
with four named grid areas.
The head area spans both columns and the first row of the grid.
The grid-template-areas property creates implicit named lines from the named grid areas in the template.
For each named grid areafoo, four implicit named lines are created:
two named foo-start, naming the row-start and column-start lines of the named grid area,
and two named foo-end, naming the row-end and column-end lines of the named grid area.
These named lines behave just like any other named line,
except that they do not appear in the value of grid-template-rows/grid-template-columns.
Even if an explicit line of the same name is defined,
the implicit named lines are just more lines with the same name.
Sets grid-template-rows to the <track-size>s following each string
(filling in auto for any missing sizes),
and splicing in the named lines defined before/after each size.
This syntax allows the author to align track names and sizes inline with their respective grid areas.
grid-template: auto 1fr auto /
(header-top) "a a a" (header-bottom)
(main-top) "b b b" 1fr (main-bottom);
is equivalent to
grid-template-columns: auto 1fr auto;
grid-template-rows: (header-top) auto (header-bottom main-top) 1fr (main-bottom);
grid-template-areas: "a a a"
"b b b";
Note: The grid shorthand accepts the same syntax,
but also resets the implicit grid properties to their initial values.
Unless authors want those to cascade in separately,
it is therefore recommended to use grid instead of grid-template.
If a grid item is positioned into a row or column that is not explicitly sized
by grid-template-rows or grid-template-columns,
implicit grid tracks are created to hold it.
This can happen either by explicitly positioning into a row or column that is out of range,
or by the auto-placement algorithm creating additional rows or columns.
The grid-auto-columns and grid-auto-rows properties specify the size of such implicitly-created tracks.
The auto-placement algorithm places items
by filling each row in turn,
adding new rows as necessary.
If neither row nor column is provided,
row is assumed.
column
The auto-placement algorithm places items
by filling each column in turn,
adding new columns as necessary.
dense
If specified, the auto-placement algorithm uses a “dense” packing algorithm,
which attempts to fill in holes earlier in the grid if smaller items come up later.
This may cause items to appear out-of-order,
when doing so would fill in holes left by larger items.
If omitted, a “sparse” algorithm is used,
where the placement algorithm only ever moves “forward” in the grid when placing items,
never backtracking to fill holes.
This ensures that all of the auto-placed items appear “in order”,
even if this leaves holes that could have been filled by later items.
Note: A future level of this module is expected to add a value that flows auto-positioned items together into a single “default” cell.
Auto-placement takes grid items in order-modified document order.
In the following example, there are three columns, each auto-sized to their contents.
No rows are explicitly defined.
The grid-auto-flow property is row
which instructs the grid to search across its three columns starting with the first row,
then the next,
adding rows as needed until sufficient space is located to accommodate the position of any auto-placed grid item.
A form arranged using automatic placement.
<style type="text/css">
form {
display: grid;
/* Define three columns, all content-sized,
and name the corresponding lines. */
grid-template-columns: (labels) auto (controls) auto (oversized) auto;
grid-auto-flow: row;
}
form > label {
/* Place all labels in the "labels" column and
automatically find the next available row. */
grid-column: labels;
grid-row: auto;
}
form > input, form > select {
/* Place all controls in the "controls" column and
automatically find the next available row. */
grid-column: controls;
grid-row: auto;
}
#department {
/* Auto place this item in the "oversized" column
in the first row where an area that spans three rows
won’t overlap other explicitly placed items or areas
or any items automatically placed prior to this area. */
grid-column: oversized;
grid-row: span 3;
}
/* Place all the buttons of the form
in the explicitly defined grid area. */
#buttons {
grid-row: auto;
/* Ensure the button area spans the entire grid element
in the row axis. */
grid-column: 1 / -1;
text-align: end;
}
</style>
<form>
<label for="firstname">First name:</label>
<input type="text" id="firstname" name="firstname" />
<label for="lastname">Last name:</label>
<input type="text" id="lastname" name="lastname" />
<label for="address">Address:</label>
<input type="text" id="address" name="address" />
<label for="address2">Address 2:</label>
<input type="text" id="address2" name="address2" />
<label for="city">City:</label>
<input type="text" id="city" name="city" />
<label for="state">State:</label>
<select type="text" id="state" name="state">
<option value="WA">Washington</option>
</select>
<label for="zip">Zip:</label>
<input type="text" id="zip" name="zip" />
<div id="department">
<label for="department">Department:</label>
<select id="department" name="department" multiple>
<option value="finance">Finance</option>
<option value="humanresources">Human Resources</option>
<option value="marketing">Marketing</option>
</select>
</div>
<div id="buttons">
<button id="cancel">Cancel</button>
<button id="back">Back</button>
<button id="next">Next</button>
</div>
</form>
The grid property is a shorthand that sets
all of the explicit grid properties
(grid-template-rows, grid-template-columns, and grid-template-areas)
as well as all the implicit grid properties
(grid-auto-rows, grid-auto-columns, and grid-auto-flow)
in a single declaration.
If <‘grid-auto-rows’> value is omitted,
it is set to the value specified for grid-auto-columns.
Other omitted values are set to their initial values.
Note: Note that you can only specify the explicit or the implicit grid properties in a single grid declaration.
The sub-properties you don’t specify are set to their initial value,
as normal for shorthands.
In addition to accepting the grid-template shorthand syntax for setting up the explicit grid,
the grid shorthand can also easily set up parameters for an auto-formatted grid.
For example, grid: row 1fr; is equivalent to
Since memory is not infinite,
UAs may clamp the the possible size of the grid
to within a UA-defined limit,
dropping all lines outside that limit.
If a grid item spans outside this limit,
its span must be clamped to the last line of the limited grid.
If a grid item is placed outside this limit,
its span must be truncated to 1
and the item repositioned into the last grid track on that side of the grid.
A definite value for any two of Start, End, and Span in a given dimension implies a definite value for the third.
The following table summarizes the conditions under which a grid position or span is definite or automatic:
Position
Span
Definite
At least one specified line
Explicit, implicit, or defaulted span. Note: Non-subgrids default to 1.
article {
grid-area: main;
/* Places item into the named area "main". */
}
An item can also be partially aligned with a named grid area,
with other edges aligned to some other line:
.one {
grid-row-start: main;
/* Align the row-start edge to the start edge of the "main" named area. */
}
9.1.2.
Numeric Indexes and Spans
Grid items can be positioned and sized by number,
which is particularly helpful for script-driven layouts:
.two {
grid-row: 2; /* Place item in the second row. */
grid-column: 3; /* Place item in the third column. */
/* Equivalent to grid-area: 2 / 3;
}
By default, a grid item has a span of 1.
Different spans can be given explicitly:
.three {
grid-row: 2 / span 5;
/* Starts in the 2nd row,
spans 5 rows down (ending in the 7th row). */
}
.four {
grid-row: span 5 / 7;
/* Ends in the 7th row,
spans 5 rows up (starting in the 2nd row). */
}
Note: Note that grid indexes are writing mode relative.
For example, in a right-to-left language like Arabic,
the first column is the rightmost column.
9.1.3.
Named Lines and Spans
Instead of counting lines by number,
named lines can be referenced by their name:
.five {
grid-column: first / middle;
/* Span from line "first" to line "middle". */
}
Note: Note that if a named grid area and a named line have the same name,
the placement algorithm will prefer to use named grid area’s edge instead.
If there are multiple lines of the same name,
they effectively establish a named set of grid lines,
which can be exclusively indexed by filtering the placement by name:
.six {
grid-row: text 5 / text 7;
/* Span between the 5th and 7th lines named "text". */
grid-row: text 5 / span text 2;
/* Same as above. */
}
9.1.4.
Auto Placement
A grid item can be automatically placed into the next available empty grid cell,
growing the grid if there’s no space left.
.eight {
grid-area: auto; /* Initial value */
}
This can be used, for example, to list a number of sale items on a catalog site
in a grid pattern.
Auto-placement can be combined with an explicit span,
if the item should take up more than one cell:
.nine {
grid-area: span 2 / span 3;
/* Auto-placed item, covering two rows and three columns. */
}
Whether the auto-placement algorithm searchs across and adds rows,
or searches across and adds columns,
is controlled by the grid-auto-flow property.
Note: By default, the auto-placement algorithm looks linearly through the grid without backtracking;
if it has to skip some empty spaces to place a larger item,
it will not return to fill those spaces.
To change this behavior,
specify the dense keyword in grid-auto-flow.
9.1.5.
Auto Sizing Subgrids
A subgrid without a definite grid span is sized to its implicit grid,
i.e. all of its items within it are first placed into its own grid,
and its span is the resulting size of its grid.
For example, a subgrid spanning two columns can be given an auto-spanning block size:
.adverts {
grid: subgrid;
grid-column: span 2;
}
If it contains 10 auto-placed items, it will span 5 rows in its parent grid.
Note: Since auto-spanning subgrids determine their span before being positioned,
they can also be auto-positioned.
The above example would auto-place the .adverts block,
if no further rules specified its position.
Contributes the Nth grid line to the grid item’s placement.
If a negative integer is given,
it instead counts in reverse,
starting from the end edge of the explicit grid.
If a name is given as a <custom-ident>,
only lines with that name are counted.
If not enough lines with that name exist,
all lines in the implicit grid are assumed to have that name for the purpose of finding this position.
A <integer> value of zero makes the declaration invalid.
Contributes a grid span to the grid item’s placement
such that the corresponding edge of the grid item’s grid area is N lines from its opposite edge.
If a name is given as a <custom-ident>,
only lines with that name are counted.
If not enough lines with that name exist,
all lines in the implicit grid are assumed to have that name for the purpose of counting this span.
If the <integer> is omitted, it defaults to 1.
Negative integers or zero are invalid.
Given a single-row, 8-column grid and the following 9 named lines:
1 2 3 4 5 6 7 8 9
+--+--+--+--+--+--+--+--+
| | | | | | | | |
A B C A B C A B C
| | | | | | | | |
+--+--+--+--+--+--+--+--+
The following declarations place the grid item between the lines indicated by index:
grid-column-start: 4; grid-column-end: auto;
/* Line 4 to line 5 */
grid-column-start: auto; grid-column-end: 6;
/* Line 5 to line 6 */
grid-column-start: C; grid-column-end: C -1;
/* Line 3 to line 9 */
grid-column-start: C; grid-column-end: span C;
/* Line 3 to line 6 */
grid-column-start: span C; grid-column-end: C -1;
/* Line 6 to line 9 */
grid-column-start: span C; grid-column-end: span C;
/* Error: The end span is ignored, and an auto-placed
item can’t span to a named line.
Equivalent to grid-column: span 1;. */
grid-column-start: 5; grid-column-end: C -1;
/* Line 5 to line 9 */
grid-column-start: 5; grid-column-end: span C;
/* Line 5 to line 6 */
grid-column-start: 8; grid-column-end: 8;
/* Error: line 8 to line 9 */
grid-column-start: B 2; grid-column-end: span 1;
/* Line 5 to line 6 */
If an absolutely positioned element’s containing block
is generated by a grid container,
its containing block edges are the edges of the element’s grid area
as given by its grid-placement properties.
In this case, an auto value for a grid-placement property
contributes the corresponding padding edge of the grid container as a line.
(Thus, by default, the containing block will correspond to the padding edges of the grid container.)
The offset properties (top/right/bottom/left)
then indicate offsets inwards from the corresponding edges
of the resulting containing block, as normal.
Note: Note that, while absolutely-positioning an element to a grid container
does allow it to align to that container’s grid lines,
such elements
do not take up space or otherwise participate in the layout of the grid.
.grid {
grid: 10rem 10rem 10rem 10rem / 1fr 1fr 1fr 1fr;
/* 4 columns of 10rem each,
4 equal-height rows filling the grid container */
justify-content: center;
/* center the grid horizontally within the grid container */
position: relative;
/* Establish abspos containing block */
}
.abspos {
grid-row-start: 1; /* 1st grid row line = top of grid container */
grid-row-end: span 2; /* 3rd grid row line */
grid-column-start: 3; /* 3rd grid col line */
grid-column-end: auto; /* right padding edge */
/* Containing block covers the top right quadrant of the grid container */
position: absolute;
top: 70px;
bottom: 40px;
left: 100px;
right: 30px;
}
The following grid item placement algorithm
resolves automatic positions of grid items into definite positions,
ensuring that every grid item has a well-defined grid area to lay out into.
(Grid spans need no special resolution;
if they’re not explicitly specified,
they default to either 1 or,
for subgrids,
the size of their explicit grid.)
Note: This algorithm can result in the creation of new rows or columns in the implicit grid,
if there is no room in the explicit grid to place an auto-positioned grid item.
Every grid cell
(in both the explicit and implicit grids)
can be occupied or unoccupied.
A cell is occupied
if it’s covered by a named grid area,
or by the grid area of a grid item with a definite grid position;
otherwise,
the cell is unoccupied.
A cell’s occupied/unoccupied status can change during this algorithm.
To aid in clarity,
this algorithm is written with the assumption that grid-auto-flow
has row specified.
If it is instead set to column,
swap all mentions of rows and columns, inline and block, etc. in this algorithm.
1. Process the items locked to a given row.
For each grid item with a definite row position
(that is, the grid-row-start and grid-row-end properties define a definite grid position),
in order-modified document order:
: “sparse” packing (omitted dense keyword)
::
Set the column-start line of its placement
to the earliest (smallest positive index) line index
that ensures this item’s grid area will not overlap any occupied grid cells
and that is past any grid items previously placed in this row by this step.
: “dense” packing (dense specified)
::
Set the column-start line of its placement
to the earliest (smallest positive index) line index
that ensures this item’s grid area will not overlap any occupied grid cells.
2. Determine the number of columns in the implicit grid.
Set the number of columns in the implicit grid to the larger of:
* The number of columns in the explicit grid.
* Among all the items with a definite column position
(explicitly positioned items, items positioned in the previous step, and items not yet positioned but with a definite column)
the largest positive column-end line index,
minus 1.
* The largest column span of all items.
The number of columns needed is 6.
The #grid-item element’s column-start line is index 4,
so its span ensures that it’s column-end line will be index 7.
This requires 7 - 1 = 6 columns to hold,
which is larger than the explicit grid’s 5 columns.
3. Position the remaining grid items.
The auto-placement cursor defines the current “insertion point” in the grid,
specified as a pair of row and column grid lines.
Initially the auto-placement cursor is specified with a row and column position both equal to 1.
The grid-auto-flow value in use determines how to position the items:
: “sparse” packing (omitted dense keyword)
:: For each grid item that hasn’t been positioned by the previous steps,
in order-modified document order:
: If the item has a definite column position:
::
1. Set the column position of the cursor to be equal to the column-start line index of the grid item.
If this is less than the previous column position of the cursor,
increment the row position by 1.
2. Increment the cursor’s row position until a value is found
where the grid item does not overlap any occupied grid cells
(creating new rows in the implicit grid as necessary).
3. Set the item’s row-start line to the cursor’s row position.
(Implicitly setting the item’s row-end line according to its span, as well.)
: If the item has an automatic grid position in both axes:
::
1. Increment the column position of the auto-placement cursor
until either this item’s grid area does not overlap any occupied grid cells,
or the cursor’s column position,
plus the item’s column span,
overflow the number of columns in the implicit grid,
as determined earlier in this algorithm.
2. If a non-overlapping position was found in the previous step,
set the item’s row-start and column-start lines to the cursor’s position.
Otherwise,
increment the auto-placement cursor’s row position
(creating new rows in the implicit grid as necessary),
set its column position to 1,
and return to the previous step.
: “dense” packing (dense specified)
:: For each grid item that hasn’t been positioned by the previous steps,
in order-modified document order:
: If the item has a definite column position:
::
1. Set the row position of the cursor to 1.
Set the column position of the cursor to be equal to the column-start line index of the grid item.
2. Increment the auto-placement cursor’s row position until a value is found
where the grid item does not overlap any occupied grid cells
(creating new rows in the implicit grid as necessary).
3. Set the item’s row-start line index to the cursor’s row position.
(Implicitly setting the item’s row-end line according to its span, as well.)
: If the item has an automatic grid position in both axes:
::
1. Set the cursor’s row and column positions both to 1.
2. Increment the column position of the auto-placement cursor
until either this item’s grid area does not overlap any occupied grid cells,
or the cursor’s column position,
plus the item’s column span,
overflow the number of columns in the implicit grid,
as determined earlier in this algorithm.
3. If a non-overlapping position was found in the previous step,
set the item’s row-start and column-start lines to the cursor’s position.
Otherwise,
increment the auto-placement cursor’s row position
(creating new rows in the implicit grid as necessary),
set its column position to 1,
and return to the previous step.
10.
Alignment
After a grid container’s grid tracks have been sized,
and the dimensions of all grid items are finalized,
grid items can be aligned within their grid areas.
The margin properties can be used to align items in a manner similar to,
but more powerful than,
what margins can do in block layout.
Grid items also respect the alignment properties from the Box Alignment spec,
which allow easy keyword-based alignment of items in both the row axis and column axis.
By default,
grid items stretch to fill their grid area.
However, if justify-self or align-self compute to a value other than stretch
or margins are auto,
grid items will auto-size to fit their contents.
This section is non-normative.
The normative definition of how margins affect grid items is in §11
Grid Sizing.
Auto margins on grid items have an effect very similar to auto margins in block flow:
During calculations of grid track sizes, auto margins are treated as 0.
Auto margins absorb positive free space
prior to alignment via the alignment properties
(defined in the next sections).
Overflowing elements ignore their auto margins and overflow in the end directions.
Note: Note that, if free space is distributed to auto margins,
the alignment properties will have no effect in that dimension
because the margins will have stolen all the free space
left over after sizing.
Otherwise, if the grid container has at least one grid item whose area intersects the first row/column,
and the first such grid item (in order-modified grid order) has a baseline
parallel to the relevant axis,
the grid container’s baseline is that baseline.
Otherwise, the grid container’s baseline is synthesized
from the first item’s (in order-modified grid order) content box,
or, failing that, from the grid container’s content box.
A grid item participates in baseline alignment in a particular dimension
if its value for align-self or justify-self, as appropriate, is baseline
and its inline axis is parallel to that dimension.
order-modified grid order is the order in which
grid items are encountered when traversing the grid’s grid cells,
in row-major order if calculating the inline-axis baseline,
or in column-major order if calculating the block-axis baseline.
If two items are encountered at the same time,
they are taken in order-modified document order.
When calculating the baseline according to the above rules,
if the box contributing a baseline has an overflow value that allows scrolling,
the box must be treated as being in its initial scroll position
for the purpose of determining its baseline.
When determining the baseline of a table cell,
a grid container provides a baseline just as a line box or table-row does. [CSS21]
11.
Grid Sizing
This section defines the grid sizing algorithm,
which determines the size of all grid tracks
and, by extension, the entire grid.
Each track has specified minimum and
maximumsizing functions
(which may be the same).
Each sizing function is either:
Finally, the grid container is sized
using the resulting size of the grid as its content size,
and the tracks are aligned within the grid container
according to the align-content and justify-content properties.
Note: This can introduce extra space within or between tracks.
(When introducing space within tracks,
only tracks with an intrinsicmax track sizing function accept space.)
Once the size of each grid area is thus established,
the grid items are laid out into their respective containing blocks.
11.2.
Track Sizing Terminology
min track sizing function
If the track was sized with a minmax() function,
this is the first argument to that function.
Otherwise, it’s the track’s sizing function.
max track sizing function
If the track was sized with a minmax() function,
this is the second argument to that function.
Otherwise, it’s the track’s sizing function.
The remainder of this section is the track sizing algorithm,
which calculates from the min and max track sizing functions
the used track size.
Each track has a base size,
a <length> which grows throughout the algorithm
and which will eventually be the track’s final size,
and a growth limit,
a <length> which provides a desired maximum size for the base size.
There are 4 steps:
This step resolves intrinsic track sizing functions to absolute lengths.
First it resolves those sizes based on items that are contained wholly within a single track.
Then it gradually adds in the space requirements of items that span multiple tracks,
evenly distributing the extra space across those tracks
insofar as possible.
When the grid container is being sized under a min-content constraint,
a track with a flexible min track sizing function
is treated as if its min track sizing function was min-content
for the purposes of this step.
This seems correct, but should be checked because it wasn’t in the original algorithm.
Note: There is no single way to satisfy these constraints
when items span across multiple tracks.
This algorithm embodies a number of heuristics
which have been seen to deliver good results on real-world use-cases,
such as the "game" examples earlier in this specification.
This algorithm may be updated in the future
to take into account more advanced heuristics as they are identified.
Size tracks to fit non-spanning items:
For each track with an intrinsic track sizing function,
consider the items in it with a span of 1:
For auto minimums:
If the track has an automin track sizing function,
set its base size
to the maximum of the items’ outer minimum sizes,
as specified by their respective min-width or min-height properties
(whichever matches the relevant axis).
Repeat incrementally for items with greater spans until all items have been considered.
If any track still has an infinite growth limit
(because, for example, it had no items placed in it),
set its growth limit to its base size.
To distribute extra space
by increasing the affected sizes of a set of tracks
as required by a set of intrinsic size contributions,
Maintain separately for each affected base size or growth limit
an amount of planned increase.
(This prevents the size increases from becoming order-dependent.)
For each considered item,
Find the space to distribute:
Subtract the corresponding size (base size or growth limit) of every spanned track
from the item’s size contribution to find the item’s remaining size contribution.
(For infinite growth limits, substitute the track’s base size.)
This is the space to distribute. Floor it at zero.
Distribute space to base sizes up to growth limits:
Distribute the space equally to the planned increase of each spanned track with an affected size,
freezing tracks as their planned size reaches their growth limits
(and continuing to grow the unfrozen tracks as needed).
If a track was marked as infinitely growable for this phase,
treat its growth limit as infinite for this calculation
(and then unmark it).
Note: If the affected size was a growth limit,
this step has no effect.
Distribute space beyond growth limits:
If space remains after all tracks are frozen,
unfreeze and continue to distribute space to…
when handling any intrinsic growth limit:
all affected tracks.
Update the tracks' affected sizes
by folding in the calculated increase
so that the next round of space distribution will account for the increase.
(If the affected size is infinite,
set it to the track’s base size plus the calculated increase.)
Note: When this step is complete,
all intrinsic base sizes and growth limits
will have been resolved to absolute lengths.
This step sizes flexible tracks
using the largest value it can assign to an fr
without exceeding the available space.
First, find the used flex fraction:
For each flexible track,
if the product of the used flex fraction and the track’s flex factor
is greater than the track’s base size,
set its base size to that product.
11.7.1.
Find the Size of an fr
This algorithm finds the largest size that an fr unit can be
without exceeding the target size.
It must be called with a set of grid tracks
and some quantity of space to fill.
If the product of the hypothetical fr size and a flexible track’s flex factor
is less than the track’s base size,
restart this algorithm
treating all such tracks as inflexible.
Grid containers can break across pages
between rows
and inside items.
The break-* properties apply to grid containers
as normal for the formatting context in which they participate.
This section defines how they apply to grid items
and the contents of grid items.
The following breaking rules refer to the fragmentation container as the “page”.
The same rules apply to any other fragmentation containers.
(Substitute “page” with the appropriate fragmentation container type as needed.)
See the CSS3 Fragmentation Module [CSS3-BREAK].
The exact layout of a fragmented grid container is not defined in this level of Grid Layout.
However, breaks inside a grid container are subject to the following rules:
The break-before and break-after properties on flex items
are propagated to their grid row.
The break-before property on the first row
and the break-after property on the last row
are propagated to the grid container.
A forced break inside a grid item effectively increases the size of its contents;
it does not trigger a forced break inside sibling items.
When a grid container is continued after a break,
the space available to its grid items
(in the block flow direction of the fragmentation context)
is reduced by the space consumed by grid container fragments on previous pages.
The space consumed by a grid container fragment is
the size of its content box on that page.
If as a result of this adjustment the available space becomes negative,
it is set to zero.
Aside from the rearrangement of items imposed by the previous point,
UAs should attempt to minimize distortation of the grid container
with respect to unfragmented flow.
12.1.
Sample Fragmentation Algorithm
This is just a rough draft.
This section needs to be severely cross-checked with the [CSS3-FLEXBOX] algorithm.
Feedback overall is welcome; please reference the rules above instead as implementation guidance.
Layout the grid following the §11
Grid Sizing by using the
fragmentainer box width and assume unlimited height. During this step all grid-rowauto and fr values must be resolved.
Layout the grid container using the values resolved in the previous step.
If a grid area dimensions change due to fragmentation (do not include items that
span rows in this decision), increase the grid row as necessary for rows that either:
have a content min track sizing function.
are in a grid that does not have an explicit height and the grid row is flexible.
If the grid height is auto, the height of the grid should be the sum of the final
row sizes.
If a grid area overflows the grid container due to margins being collapsed during
fragmentation, extend the grid container to contain this grid area (this step is
necessary in order to avoid circular layout dependencies due to fragmentation).
If the grid’s height is specified, steps three and four may cause the grid rows to
overflow the grid.
Acknowledgements
This specification is made possible by input from
Erik Anderson,
Rossen Atanassov,
Arron Eicholz,
Sylvain Galineau,
Markus Mielke,
John Jansen,
Chris Jones,
Kathy Kam,
Veljko Miljanic,
Peter Salas,
Christian Stockwell,
Eugene Veselov,
and the CSS Working Group members.
Thanks to Eliot Graff for editorial input.
Note: The following is a more direct translation of the
original Microsoft editors' track sizing algorithm,
from which the current algorithm is derived.
It follows the original algorithm structure
without being as programmatic in its language.
It is preserved here to aid in review of the current specification
(and will be removed in the next revision).
This algorithm is run multiple times,
once for each set of grid items with a particular span count,
and each time it moves through four phases,
each one addressing one combination of min-content or max-content
as a min track sizing function or max track sizing function.
Starting from the set of all grid items in the grid,
remove any with a span count greater than one
which span a track with a <flex>max track sizing function.
Of the remaining,
sort them into groups according to their span count,
and order the groups in ascending order of span count.
For each group, in order,
perform the following steps four times:
Initialize variables.
Let each item’s needed space be:
In phase 1
The min-content size of the item,
minus the sum of the base sizes of the grid tracks it spans.
In phase 2
The max-content size of the item,
minus the sum of the base sizes of the grid tracks it spans.
In phase 3
The min-content size of the item,
minus the sum of the growth limits of the grid tracks it spans
(or, if the growth limit is infinite, the base size).
In phase 4
The max-content size of the item,
minus the sum of the growth limits of the grid tracks it spans
(or, if the growth limit is infinite, the base size).
Conformance requirements are expressed with a combination of
descriptive assertions and RFC 2119 terminology. The key words "MUST",
"MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this
document are to be interpreted as described in RFC 2119.
However, for readability, these words do not appear in all uppercase
letters in this specification.
All of the text of this specification is normative except sections
explicitly marked as non-normative, examples, and notes. [RFC2119]
Examples in this specification are introduced with the words "for example"
or are set apart from the normative text with class="example",
like this:
This is an example of an informative example.
Informative notes begin with the word "Note" and are set apart from the
normative text with class="note", like this:
Note, this is an informative note.
Advisements are normative sections styled to evoke special attention and are
set apart from other normative text with <strong class="advisement">, like
this:
UAs MUST provide an accessible alternative.
Conformance classes
Conformance to this specification
is defined for three conformance classes:
A style sheet is conformant to this specification
if all of its statements that use syntax defined in this module are valid
according to the generic CSS grammar and the individual grammars of each
feature defined in this module.
A renderer is conformant to this specification
if, in addition to interpreting the style sheet as defined by the
appropriate specifications, it supports all the features defined
by this specification by parsing them correctly
and rendering the document accordingly. However, the inability of a
UA to correctly render a document due to limitations of the device
does not make the UA non-conformant. (For example, a UA is not
required to render color on a monochrome monitor.)
An authoring tool is conformant to this specification
if it writes style sheets that are syntactically correct according to the
generic CSS grammar and the individual grammars of each feature in
this module, and meet all other conformance requirements of style sheets
as described in this module.
Partial implementations
So that authors can exploit the forward-compatible parsing rules to
assign fallback values, CSS renderers must
treat as invalid (and ignore
as appropriate) any at-rules, properties, property values, keywords,
and other syntactic constructs for which they have no usable level of
support. In particular, user agents must not selectively
ignore unsupported component values and honor supported values in a single
multi-value property declaration: if any value is considered invalid
(as unsupported values must be), CSS requires that the entire declaration
be ignored.
Experimental implementations
To avoid clashes with future CSS features, the CSS2.1 specification
reserves a prefixed
syntax for proprietary and experimental extensions to CSS.
Prior to a specification reaching the Candidate Recommendation stage
in the W3C process, all implementations of a CSS feature are considered
experimental. The CSS Working Group recommends that implementations
use a vendor-prefixed syntax for such features, including those in
W3C Working Drafts. This avoids incompatibilities with future changes
in the draft.
Non-experimental implementations
Once a specification reaches the Candidate Recommendation stage,
non-experimental implementations are possible, and implementors should
release an unprefixed implementation of any CR-level feature they
can demonstrate to be correctly implemented according to spec.
To establish and maintain the interoperability of CSS across
implementations, the CSS Working Group requests that non-experimental
CSS renderers submit an implementation report (and, if necessary, the
testcases used for that implementation report) to the W3C before
releasing an unprefixed implementation of any CSS features. Testcases
submitted to W3C are subject to review and correction by the CSS
Working Group.
This seems correct, but should be checked because it wasn’t in the original algorithm. ↵
This is just a rough draft.
This section needs to be severely cross-checked with the [CSS3-FLEXBOX] algorithm.
Feedback overall is welcome; please reference the rules above instead as implementation guidance.
↵