Unicorn Formatting Objects (UFO), Version 1.00.01
Support for XSL Formatting Objects and Properties
HTML Back-End
Created: 29-Sep-2000
Copyright (C) 2000, Unicorn Enterprises SA
All rights reserved
1 Introduction
--------------
This document defines the subset of XSL formatting objects and
their properties as supported by UFO version 1.00.01 using the
HTML back-end.
UFO supports also TeX back-end, which is not discussed here.
The detailed description of TeX back-end features is available
as a separate document included in the product distribution:
Unicorn Formatting Objects (UFO), Version 1.00.01
Support for Formatting Objects and Properties
TeX Back-End
2 General Notes
---------------
Notational Conventions
----------------------
Known unsupported yet important features are marked with the
ISSUE prefix in this document. In most cases, the decent effort
will be made to implement them in the near future.
ISSUE: Create a summary of all current ISSUEs at the end of
this document.
Front-end and Back-end
----------------------
The UFO HTML front-end (written in C++) generates the HTML 4.0
output. The Web browser that implements HTML 4.0 can be used
as a back-end to render the generated document. Since the
Cascading Stylesheets Level 2 (CSS2) technology is extensively
used, the browser with the decent support for CSS2 is required.
Version of XSL Specification
----------------------------
The current release is based on the W3C specification
"Extensible Stylesheet Language (XSL) Version 1.0"
W3C Working Draft 27 March 2025
(http://www.w3c.org/TR/2000/WD-xsl-20000327)
No claims are made about the conformance.
Use of CSS2 Specification
-------------------------
XSL specification does not define many important features.
Instead, explicit (and in some cases implicit) references are
made to CSS2 specification. Implementation of such features
is based on the W3C specification
"Cascading Stylesheets, Level 2 (CSS2)"
W3C Recommendation 12 May 2024
(http://www.w3c.org/TR/1998/REC-CSS2-19980512)
Formatting Objects, Properties and Property Values
--------------------------------------------------
The following formatting objects are currently supported:
fo:root
fo:declarations
fo:page-sequence
fo:layout-master-set
fo:page-sequence-master
fo:single-page-master-reference
fo:simple-page-master
fo:region-body
fo:flow
fo:static-content
fo:title
fo:block
fo:character
fo:external-graphic
fo:inline
fo:table-and-caption
fo:table
fo:table-column
fo:table-caption
fo:table-header
fo:table-footer
fo:table-body
fo:table-row
fo:table-cell
fo:list-block
fo:list-item
fo:list-item-body
fo:list-item-label
fo:simple-link
fo:wrapper
For all other formatting objects, UFO implements the appropriate
fallbacks according to provisions of XSL WD (Chapter 8,
"Conformance").
Detailed discussion of support for all formatting objects can be
found in the following sections of this document. For each object
type the list of supported properties is given as well.
For unsupported formatting objects, the fallback implementation
is described.
Units of Measure
----------------
All units of measure defined by XSL except 'px' (pixels) are
supported. In the internal calculations as well as in the output
TeX code, for all properties except 'font-size', units of measure
are converted to millimeters. For the 'font-size' property, units
of measure are converted to points.
Color Values
------------
Hexadecimal color values having the format
#[a-fA-F0-9]
are supported. Maximum of 6 hexadecimal digits allowed. These
values represent RGB colors in the way similar to one described in
HTML 4.0 specification.
The following named color values are supported:
aqua #00FFFF
black #000000
blue #0000FF
fuchsia #FF00FF
gray #808080
green #008000 [sic!]
lime #00FF00
maroon #800000
navy #000080
olive #808000
purple #800080
red #FF0000
silver #C0C0C0
teal #008080
white #FFFF00
An additional color value
orange #FF8000
is supported for interoperability with the PassiveTex package.
Percentages
-----------
Percentages in property values are supported when applicable.
Shorthand Properties
--------------------
The following shorthand properties are supported
border-width
border-color
border-style
border-top
border-right
border-bottom
border-left
border
font
margin
padding
white-space
The 'vertical-align' is implemented as a normal (not a shorthand)
property.
Expressions
-----------
XSL expressions are not implemented. The only exception is the
minus sign that can precede numeric values.
Inheritance
-----------
Property inheritance is supported. A property that is implemented
in this release may be assigned to a formatting object of any type
allowed by XSL/CSS2, even if this formatting object makes no direct
use of this property. The property value may be inherited and used
by some child formatting object. In this document, properties of this
kind are mentioned explicitly only for the formatting object types
that make the direct use of them; however, for inheritance purposes
these properties are supported also for other object types when
allowed by XSL/CSS2.
Writing Modes
-------------
The 'writing-mode' property is not supported.
By default, the 'lr-tb' writing mode is assumed. The relative margin,
border and padding properties that contain 'before', 'after',
'start' and 'end' in their names are interpreted according to this
writing mode.
Margin Properties
-----------------
The following margin properties are supported:
margin-top
margin-bottom
margin-left
margin-right
margin-before
margin-after
margin-start
margin-end
space-before
space-before.optimum
space-after
space-after.optimum
In the sections that describe properties supported for each
formatting object type, these properties are referenced collectively
as "Margin Properties".
Properties 'space-before' and 'space-before.optimum' are interpreted
as corresponding to 'margin-top'; properties 'space-after' and
'space-after.optimum' are interpreted as corresponding to
'margin-bottom'.
Margin collapsing/space resolution is not supported.
ISSUE: Margin collapsing/space resolution is an important
feature. It should be implemented in the near future.
Border Properties
-----------------
The following border properties are supported:
border-top-style
border-bottom-style
border-left-style
border-right-style
border-before-style
border-after-style
border-start-style
border-end-style
border-top-color
border-bottom-color
border-left-color
border-right-color
border-before-color
border-after-color
border-start-color
border-end-color
border-top-width
border-bottom-width
border-left-width
border-right-width
border-before-width
border-after-width
border-start-width
border-end-width
In the sections that describe properties supported for each
formatting object type, these properties are referenced collectively
as "Border Properties".
Padding Properties
------------------
The following padding properties are supported:
padding-top
padding-bottom
padding-left
padding-right
padding-before
padding-after
padding-start
padding-end
In the sections that describe properties supported for each
formatting object type, these properties are referenced collectively
as "Padding Properties".
Font Properties
---------------
The following font properties are supported:
font-family
font-style
font-variant
font-weight
font-size
In the sections that describe properties supported for each
formatting object type, these properties are referenced collectively
as "Font Properties".
The following generic font families are supported
serif Times
sans-serif Helvetica
cursive ZapfChancery
monospace Courier
The 'fantasy' generic font family is not supported since there
is no true fantasy font among 35 standard PostScript fonts.
Properties Related to White Spaces
----------------------------------
The following properties related to white spaces are supported:
linefeed-treatment
space-treatment
white-space-collapse
The property 'wrap-option' is supported in a special way.
If this property has the value of 'no-wrap', it is interpreted
as if 'linefeed-treatment' would be set to 'preserve' (the
actual value of 'linefeed-treatment' is ignored in this case).
3. Declaration and Pagination and Layout Formatting Objects
-----------------------------------------------------------
Introduction
------------
The HTML back-end of UFO processor was designed primarily for
viewing documents using non-paged devices. Therefore, features
related to pages are not supported by HTML back-end.
If a complex page-sequence-master is required for a given
page-sequence, the first simple-page-master referenced in
the content of the complex page-sequence-master will be
used for the actual rendering of this page-sequence.
fo:root
-------
No individual properties supported.
fo:declarations
---------------
No individual properties supported.
fo:color-profile
----------------
This formatting object class is handled with the fallback.
fo:page-sequence
----------------
The following properties are supported:
master-name
fo:layout-master-set
--------------------
No individual properties supported.
fo:page-sequence-master
-----------------------
The following properties are supported:
master-name
This formatting object class is handled with the fallback.
The page-master referenced in the first child is used.
fo:single-page-master-reference
-------------------------------
The following properties are supported:
master-name
fo:repeatable-page-master-reference
-----------------------------------
The following properties are supported:
master-name
This formatting object class is handled with the fallback.
The page-master referenced in the first child is used.
fo:repeatable-page-master-alternatives
--------------------------------------
This formatting object class is handled with the fallback.
The page-master referenced in the first
'fo:conditional-page-master-reference' child is used.
The following properties are supported:
maximum-repeats
fo:conditional-page-master-reference
------------------------------------
This formatting object class is handled with the fallback.
The page-master referenced in the first
'fo:conditional-page-master-reference' child is used.
The following properties are supported:
master-name
fo:simple-page-master
---------------------
The following properties are supported:
master-name
page-width
Margin Properties
fo:region-body
--------------
The following properties are supported:
region-name
Margin Properties
fo:region-before
----------------
This formatting object class is handled with the fallback.
The content of the corresponding 'fo:static-content'
object is rendered before content of the body region
The following properties are supported:
region-name
fo:region-after
---------------
This formatting object class is handled with the fallback.
The content of the corresponding 'fo:static-content'
object is rendered after content of the body region
The following properties are supported:
region-name
fo:region-start
---------------
This formatting object class is handled with the fallback.
The content of the corresponding 'fo:static-content'
object is rendered before content of the body region
The following properties are supported:
region-name
fo:region-end
-------------
This formatting object class is handled with the fallback.
The content of the corresponding 'fo:static-content'
object is rendered after content of the body region
The following properties are supported:
region-name
fo:flow
-------
No individual properties supported. The 'flow-name' property,
if specified, will be ignored by the front-end.
fo:static-content
-----------------
The following properties are supported:
flow-name
fo:title
--------
No individual properties supported.
Content of the first 'fo:title' formatting object in a document
is interpreted as the title of generated HTML document.
4. Block-level Formatting objects
---------------------------------
Introduction
------------
Algorithms described in CSS2 are used to calculate vertical
and horizontal parameters of block objects (height, width,
margins, border-widths, paddings); the support for 'auto'
property values is provided when appropriate.
fo:block
--------
The following properties are supported:
height
width
min-height
min-width
max-height
max-width
background-color
Margin Properties
Border Properties
Padding Properties
Font Properties
color
line-height
linefeed-treatment
space-treatment
text-align
text-indent
white-space-collapse
wrap-option
fo:block-container
------------------
This formatting object class is handled with the fallback.
The processor displays indication that content cannot be correctly
rendered.
5. Inline-level Formatting Objects
----------------------------------
fo:bidi-override
----------------
This formatting object class is handled with the fallback.
The processor displays indication that content cannot be correctly
rendered.
fo:character
------------
The following properties are supported:
character
Font Properties
color
fo:initial-property-set
-----------------------
This formatting object class is handled with the fallback.
Any properties specified on this object are ignored.
fo:external-graphic
-------------------
The following properties are supported:
height
width
content-height
content-width
text-align
vertical-align
src
fo:instream-foreign-object
--------------------------
This formatting object class is handled with the fallback.
The processor displays indication that content cannot be correctly
rendered.
fo:inline
---------
The following properties are supported:
Font Properties
color
fo:inline-container
-------------------
This formatting object class is handled with the fallback.
The processor displays indication that content cannot be correctly
rendered.
fo:leader
---------
This formatting object class is handled with the fallback.
The formatting object is ignored by the processor.
fo:page-number
--------------
This formatting object class is handled with the fallback.
The formatting object is ignored by the processor.
fo:page-number-citation
-----------------------
This formatting object class is handled with the fallback.
The processor displays indication that content cannot be correctly
rendered.
6. Table Formatting Objects
---------------------------
fo:table-and-caption
--------------------
The following properties are supported:
background-color
Margin Properties
Border Properties
Padding Properties
caption-side
fo:table
--------
The following properties are supported:
width
background-color
Margin Properties
Font Properties
color
fo:table-column
---------------
The following properties are supported:
column-width
background-color
Border Properties
fo:table-caption
----------------
The following properties are supported:
height
min-height
min-width
background-color
Border Properties
Padding Properties
fo:table-header
---------------
The following properties are supported:
background-color
Border Properties
fo:table-footer
---------------
The following properties are supported:
background-color
Border Properties
fo:table-body
-------------
The following properties are supported:
background-color
Border Properties
fo:table-row
------------
The following properties are supported:
height
background-color
Border Properties
fo:table-cell
-------------
The following properties are supported:
background-color
Border Properties
Padding Properties
Font Properties
color
linefeed-treatment
space-treatment
text-align
text-indent
white-space-collapse
wrap-option
Cells spanning several columns and/or rows are not yet implemented.
7. List Formatting Objects
--------------------------
The complete set of list formatting objects is supported.
In the current release, the horizontal layout of a list is fully
controlled by the 'margin-left', 'margin-right',
'provisional-label-separation' and
'provisional-distance-between-starts' properties as follows:
The distance between the left edge of the containing block and
the left edge of the label if equal to 'margin-left'.
The distance between the right edge of the label and the left
edge of the body is equal to 'provisional-label-separation'.
The block width is equal to the width of the containing block
minus 'margin-left' minus 'provisional-distance-between-starts'
minus 'margin-right'.
The distance between the right edge of the body and the right edge
of the containing block is equal to 'margin-right'.
fo:list-block
-------------
The following properties are supported:
Margin Properties
provisional-label-separation
provisional-distance-between-starts
fo:list-item
------------
The following properties are supported:
Margin Properties (vertical margins only)
fo:list-item-block
------------------
No individual properties supported.
Note that the 'start-indent' property, as well as 'body-start()'
function suggested by XSL WD are not supported. The XSL WD
specification on this subject appears to be somewhat controversial,
since 'start-indent' is not listed among the properties allowed for
'fo:list-item-block'.
fo:list-item-label
------------------
No individual properties supported.
Note that the 'end-indent' property, as well as 'label-end()'
function suggested by XSL WD are not supported. The XSL WD
specification on this subject appears to be somewhat controversial,
since 'end-indent' is not listed among the properties allowed for
'fo:list-item-label'.
8. Link an Multi Formatting Objects
-----------------------------------
fo:simple-link
--------------
The following properties are supported:
Font Properties
color
external-destination
internal-destination
fo:multi-switch
---------------
This formatting object class is handled with the fallback.
Contents of the first eligible multi-case formatting object
is utilized.
fo:multi-case
-------------
This formatting object is used as a wrapper for the fallback
for multi-switch.
The following properties are supported:
starting-state
fo:multi-toggle
---------------
This formatting object class is handled with the fallback.
Content is promoted to the parent formatting object.
fo:multi-properties
-------------------
This formatting object class is handled with the fallback.
Content is promoted to the parent formatting object.
fo:multi-property-set
---------------------
This formatting object class is handled with the fallback.
It is ignored by the processor.
9. Out-of-Line Formatting Objects
---------------------------------
fo:float
--------
This formatting object class is handled with the fallback.
It is placed inline.
fo:footnote
-----------
This formatting object class is handled with the fallback.
It is placed inline.
fo:footnote-body
----------------
This formatting object class is handled with the fallback.
It is placed inline.
10. Other Formatting Objects
----------------------------
fo:wrapper
----------
This formatting object may be used to specify inherited properties
for a group of formatting objects.
fo:marker
---------
This formatting object class is handled with the fallback.
It is ignored by the processor.
fo:retrieve-marker
------------------
This formatting object class is handled with the fallback.
The processor displays indication that content cannot be correctly
rendered.