8.1 Floats

8.1.1 Float definition

Using the float object, you can position out-of-line information at the before, start, or end sides of a page.

• The before floats are flowed in the before-float reference area (see Figure 8-1).

• A float creates a dimensionless anchor area in the area tree.

• The anchor is tied to the information that precedes the float in the flow.

• Out-if-line information is placed relative to the anchor

  • typically at the top or sides of the page in which the anchor is flowed.

• The content of the float is always a set of block-level constructs.

Information can be defined at the block level or at the inline level of the flow.

• The anchor is treated as a block if defined at the block level.

• The anchor is typically treated as an inline construct if defined at the inline level.

  • It is treated as a block object if the line area created by the inline constructs consists only of anchors.

• It must be defined in the body region of the page.

• It must be defined as a descendant of a relatively positioned block.

  • Absolutely positioned areas cannot have float descendants.

• It cannot have any float , footnote , or marker descendants.

The blocks of the float definition are positioned in the area tree accordingly .

• The before floats are stacked in the before-float reference area.

• The side floats are stacked in a side-float reference area.

  • This is a child of the specifying block's ancestral span reference area.

• Float content that does not float is flowed as normal content.

  • This may be the result of a faulty definition or placement.

  • A float is an area that is not normally flowed and cannot be defined within any other area that is not normally flowed (e.g. another float, a footnote, a perimeter region, an absolutely positioned block container, etc.).

• Float lengths cannot be preset and are always derived from the content of the float.

The block areas that float have no border or padding.

• Padding, border, and content rectangles are coincident.

Side floats do not overlap and are typically placed beside each other.

• They make a further incursion into the inline-progression dimension of the block.

• They can be forced to not be placed beside each other by using the clear property.

  • Different values control which floats are clear of other floats.

8.1.2 The float object

Purpose

• This is the content to be rendered towards either the before, start, or end edges of the body region regardless of where in the region the content is defined.

Content

• ( 6.10.2 ) ( %block;)+,

• child object:

  • %block; ( 6.2 ; 69).

Optional properties

• clear ( 7.18.1 ; 368),

• float ( 7.18.2 ; 376).

8.1.3 The interaction of blocks and floats

The clear property is used to prevent two side floats from being beside each other or a block-level object from being beside a float.

• It is not documented as a property within the individual block-level object descriptions.

  • It applies to all such constructs as documented in the property definition.

• The default is for side floats to continue intruding into the main reference area.

  • Use clear to start a side float back at the edge, clear of any previous float.

• The default is for the lines of a block to contour around the accumulation of side floats.

  • Use clear to start a block back at the edge, clear of any previous float.

• Those constructs with the clear value clear the float they would otherwise be beside.

Consider three situations in Figure 8-2 that illustrate the use of clear on each of floats and blocks;

• the numbers reflect the order in which the constructs are flowed;

• the thick-lined blocks with "F-" prefixes are floats;

• the thin-lined blocks with "B-" prefixes are blocks.

Figure 8-2. The clearing of slide floats by new constructs

Of note in the diagram:

• the left-most page fragment shows the default situation where side floats intrude and blocks flow around floats;

  • the second float ("F-3") is to the right of the first float ("F-1");

  • the second block ("B-4") wraps around both floats;

• the center page fragment shows the second float being clear of the first float;

  • the second block ("B-4") starts abutted to the first block ("B-2");

• the right-most page fragment shows the second block being clear of all floats;

  • the second float ("F-3") is to the right of the first float ("F-1");

  • the second block ("B-4") is clear of both floats.

The intrusion- displace property indicates the strategy of locating the start (or end) edges and indents of the lines of the block being intruded upon.

• Note that displacing the edge of a block necessarily displaces all lines in that block.

Consider three situations in Figure 8-3 that illustrate the use of intrusion-displace on a block with both text-indent and start-indent .

• " indent " respects text-indent and start-indent ;

• " block " respects text-indent but limits all lines by the width of the float;

• " line " ignores text-indent if occupied by the float, and respects start-indent .

Figure 8-3. The behavior of lines in a block next to a float