2.2.1 Summary
Allowing copyfitting on fo:flow-assignment, fo:region-body and
fo:region objects. Future revisions of the specs may include
copyfitting for other objects too.
Introducing the concept of “list of prioritized properties to be
adjusted for copyfitting”.
Adding a new property "copyfit-by-modifying" that specifies such
lists.
Exploiting range values of existing properties to specify how (and
how much) each property can be adjusted for copyfitting.
Introducing the idea of "elasticity".
Adding new values to the property "force-page-count" to model
copyfit into a fixed number of pages or a multiple of a number.
Note:
how to express alternative content:
what happens if it is
not possible?
how to express consistency and
relationships among copyfitted areas?
how to copyfit irregular shapes?
2.2.2 Copyfit: basic approach and definitions
Many options exist to copyfit content to a certain area. For
example, a user could add some space between paragraphs, widen or
narrow spaces before and after titles, images and tables, modify
the line height of some paragraphs, etc. All these fine tunings,
and their multiplicity of combinations, lead to different results,
and different users could have different preferences.
In order to give users such control, XSL-FO allows users to
express copyfitting strategies through
"copyfit properties lists".
A copyfit properties list is an ordered sequence of properties
names (or group of names) that a formatter is allowed to modify in
order to do copyfitting. The order of the names in the list
follows the priority rules described below.
Copyfit properties list can be associated to fo:objects by using
the property "copyfit-by-modifying"[@@].
The "copyfit-by-modifying"
property applies to fo:flow-assignment, fo:region and
fo:region-body in this specification. This makes possible to use
implicit flow maps and to copyfit a single flow to a single region,
multiple flows to a single region or even multiple flows to
multiple regions.
If that property is defined on both a fo:flow-assignment and a
fo:region-* involved by that assignment, the value is taken from
the fo:flow-assignment definition.
Future versions of this specification may add copyfit capabilities
to other fo:objects.
Note:
Copyfit capabilites could be useful in other contexts too.
For instance, users might be interested in copyfit text into a
block-container or into a table cell. The discussion about the
scope of copyfitting is still open.
Note:
Copyfit is activated by setting the property
"copyfit-by-modifying" of fo:flow-assignment, fo:region or
fo:region-body objects. That actually performs two logically
separated tasks: the request of copyfitting to a given area and the
definition of strategies to copyfit. Copyfitting could have been
activated by using other properties too. For instance, by
introducing a new boolean property or by extending the values of
"display-align". Such a solution is still under investigation.
Alternatively, "copyfit-by-modifying" could be said to
take effect only if display-align is "copyfit". Some
clarification is also needed about the relation between copyfitting
and vertical justification, which could be both seen as slightly
different instances of the same general concept.
Note:
The property "display-align-last" may also
need to be added if copyfitting will be activated with
"display-align" (in analogy with text-align and
text-align-last). The idea is to have a value
"relative" meaning that: if display-align is copyfit,
then the alignment of the last page, and of any page ending with a
forced break, will be "before", otherwise the value
for display-align is used for all pages.
It is important to note that “copyfit-by-modifying” only states the copyfitting strategy, and does not define the actual property ranges the application is allowed to modify. These are instead expressed (as in an XSL-FO 1.1 document) throughout the flow and its descendant formatting objects: this provides a great expressing power in a simple way, as, for example, it allows for different fo:block to have different adjusting properties.
For example: fill-by-modifying=”space-before word-spacing” means that the application is allowed to modify the actual value of the space-before and word-spacing properties. Although the “copyfit-by-modifying” property is defined in the fo:flow-assignment object, the variations are defined in the “space-before” and “word-spacing” properties of the blocks within the actual flow. In most cases values of these properties are actually inherithed. The application should try to copyfit text by choosing appropriate values for the space-before traits (using a value either greater or smaller that the .optimum one but still between the relevant .minimum and .maximum) of each block.
In fact, many FO properties (dating back to the initial XSL-FO specification) can be given a length range value, expressed using a .minimum, .optimum and .maximum components; others (allowed-height-scale, allowed-width-scale) can be given a list of numeric values; font-family can be given a list of values.
A property having a range value can create some elasticity: the dimensions of the areas generated by the affected formatting objects can stretch or shrink from an optimal value. An FO subtree is said to have inline elasticity if there are properties involved in the line building process that have some degree of elasticity; similarly, an FO subtree is said to have block elasticity if there are properties involved in the block stacking process that have some degree of elasticity. It should be noted that a length range in an inline-related property can involve both inline and block elasticity (as, for example, a variation in word-spacing may result in the creation of fewer or more lines), while a range in a block-related property only creates block elasticity.
The presence of some elasticity is the first condition to allow copyfitting. Properties with range or list values, in fact, can be adjusted in order to achieve the expected result.
On the other hand, elasticity does not automatically imply that content will be copyfitted. It may happen that properties listed in “copyfit properties list” do not have elasticity while other do. In that case the formatter cannot copyfit text and should warn the user.
If properties listed in the “copyfit properties list” do have elasiticy but the formatter is not able to copyfit text – because of syntax errors, limitated support of required copyfit strategies, etc. – the formatter should warn the user too.
An example of copyfit declaration and application is shown below:
<fo:flow flow-name="A">
<fo:block word-spacing.minimum=”1pt” word-spacing.maximum=”4pt”
line-height.minimum=”8pt” line-height.maximum=”14pt”> In the second century of the
Christian Era . . . were guarded by ancient renown and disciplined valor. </fo:block>
<fo:block word-spacing.minimum=”1pt” word-spacing.maximum=”4pt”
line-height.minimum=”8pt” line-height.maximum=”14pt”>The gentle but powerful. . . .
and devolved on the emperors all the executive powers of government. </fo:block>
<fo:block word-spacing.minimum=”1pt” word-spacing.maximum=”4pt”
line-height.minimum=”8pt” line-height.maximum=”14pt”>During a happy period of more than fourscore years . . .
to describe the prosperous condition of their empire; </fo:block>
</fo:flow>
<fo:flow flow-name="B">
<fo:block word-spacing.minimum=”1pt” word-spacing.maximum=”4pt”
line-height.minimum=”8pt” line-height.maximum=”14pt”>Quo usque tandem abutere, . . .
nihil hic munitissimus habendi senatus locus, nihil horum ora voltusque moverunt? </fo:block>
<fo:block word-spacing.minimum=”1pt” word-spacing.maximum=”4pt”
line-height.minimum=”8pt” line-height.maximum=”14pt”>Patere tua consilia non sentis. . .
Senatus haec intellegit. consul videt; hic tamen vivit. . . nostrum. </fo:block>
<fo:block word-spacing.minimum=”1pt” word-spacing.maximum=”4pt”
line-height.minimum=”8pt” line-height.maximum=”14pt”>Nos autem fortes viri . . .
in nos [omnes iam diu] machinaris. </fo:block>
</fo:flow>
<fo:flow-map flow-map-name="E1">
<fo:flow-assignment copyfit-by-modifying=”word-spacing”>
<fo:flow-source-list>
<fo:flow-name-specifier flow-name-reference="A"/>
</fo:flow-source-list>
<fo:flow-target-list>
<fo:region-name-specifier region-name-reference="R"/>
</fo:flow-target-list>
</fo:flow-assignment>
<fo:flow-assignment copyfit-by-modifying=”line-height”>
<fo:flow-source-list>
<fo:flow-name-specifier flow-name-reference="B"/>
</fo:flow-source-list>
<fo:flow-target-list>
<fo:region-name-specifier region-name-reference="S"/>
</fo:flow-target-list>
</fo:flow-assignment>
</fo:flow-map>
The two fo:flow-assignment use different strategies to copyfit.
Flow A is copyfitted by only adjusting the word-space of each block
(that will be a value between 1pt and 4pt), while flow B is
copyfitted by adjusting line-height of each block (that will be a
value between 8pt and 14pt).
Note:
The definition of “copyfit-by-modifying” in a
fo:flow-assignment object provides great flexibility to the
copyfit process. In fact, different blocks may have different
values of the same property that are all within the allowed
ranges. Though any result that satisfies the specified
constraints would conform to this specification, current
typographic practice would tend to use the available elasticity
with uniformity within the same page-sequence or, at least,
whitin the same page. So, for example, if two fo:blocks having
the same values for space-before happen to generate areas for a
copyfitted page, and the application has to use this elasticity,
the result most use will expect would have both spaces being set
to an identical value.
