[Xmlgraphics-fop Wiki] Update of "PropertyHandling/Percentages" by ManuelMall

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The following page has been changed by ManuelMall:
http://wiki.apache.org/xmlgraphics-fop/PropertyHandling/Percentages

New page:
= Percentages and Properties =
This is an attempt to summarise in an understandable fashion the rules
related to the resolution of percentages in property values. The page is
organised such that the major subheadings group a set of related rules together.
Rules are considered related if the underlying resolution algorithm is logically 
the same. Under each subheading the individual rules using the text as stated in the 
XSL-FO specification and the properties they apply to are shown.

For each property the current status of the implementation is shown.

The construction of this page was driven by the need to look at and improve the current
implementation of the percentage resolution mechanism (see http://marc.theaimsgroup.com/?l=fop-dev&m=110630658730554&w=2).

The XSL-FO rules related to determining the base value on which to perform percentage 
calculations can be put into 3 broad classes:

 1. Rules referring to properties in the fo element or its parent
 2. Rules referring to area dimensions
 3. Other rules not covered by 1. or 2.

= 1. Rules referring to properties in the fo element or parent fo element =
Percentage values in this group are resolved relative to properties on the
same or the parent element. These values can be resolved during fo tree 
construction as they do not require any input from the area tree.

Suggestion: Change the percentage implementation such that these properties
are resolved at fo tree construction time. This would allow to dispose of
the property lists earlier (see also http://marc.theaimsgroup.com/?l=fop-dev&m=110442946030972&w=2).

=== XSL-FO Rule: refer to the font size of the element itself ===
==== Properties ====
 * line-height

=== XSL-FO Rule: refer to font's em-height ===
==== Properties ====
 * text-altitude: Percentage support not configured 
 * text-depth: Percentage support not configured

=== XSL-FO Rule: refer to parent element's font size ===
==== Properties ====
 * font-size

=== XSL-FO Rule: refer to the "line-height" of the element itself ===
==== Properties ====
 * vertical-align: Percentage support not configured

=== XSL-FO Rule: refer to the corresponding height or width of the page-viewport-area ===
Although this rule refers to an area, the dimensions of a page-viewport-area are taken
straight from the corresponding page-width / page-height properties. Therefore it should
be possible to calculate these during fo tree construction.
==== Properties ====
 * extent: Percentage support not configured

=== XSL-FO Rule: refer to the "line-height" of the parent area ===
Not sure about this one - I assume taking the line-height from the parent
fo element would be OK?
==== Properties ====
 * baseline-shift: Percentage support not configured

= 2. Rules referring to dimensions of an area =
The rules in this class fall into the following groups:
 1. Rules referring to the 'closest ancestor block area'
 2. Rules referring to the 'parent area'
 3. Rules referring to the 'reference area'
 4. Rules referring to the 'area created by the element'
 5. Rules referring to tables

To resolve percentages on property values for any properties in this class access
to the area tree and the dimensions on those areas is required.

== 2.1 Rules referring to the 'closest ancestor block area' ==
The XSL-FO specification uses the definitions 'containing block' and 
'closest ancestor block area that is not a line area' interchangebly. The term 'containing block'
is used in the context of CSS derived properties while 'closest ancestor block area that 
is not a line area' is used for XSL-FO properties. Care must be taking that the design for
this rule group handles the exceptions noted in http://www.w3.org/TR/xsl/slice7.html#percrule correctly.
=== XSL-FO Rule: refer to inline-progression-dimension of closest ancestor block area that is not a line area ===
==== Properties ====
 * last-line-end-indent: Percentage support not configured
 * provisional-distance-between-starts: Percentage support not configured
 * provisional-label-separation: Percentage support not configured
 * space-end: Percentage support not configured
 * space-start: Percentage support not configured

=== XSL-FO Rule: refer to width of containing block ===
==== Properties ====
 * left: Percentage support not configured
 * right: Percentage support not configured
 * margin, margin-bottom, margin-left, margin-right, margin-top
 * max-width, min-width: Properties not implemented
 * padding, padding-after, padding-before, padding-bottom, padding-end, padding-left, padding-right, padding-start, padding-top
 * text-indent
 * width

=== XSL-FO Rule: refer to height of containing block ===
==== Properties ====
 * max-height, min-height: Properties not implemented
 * top: Percentage support not configured
 * bottom: Percentage support not configured

=== XSL-FO Rule: calculated with respect to the height of the generated box's containing block ===
==== Properties ====
 * height: Not sure its implemented correctly - XSL-FO: If the height of the containing block is not specified explicitly (i.e., it depends on content height), the value is interpreted like "auto".

=== XSL-FO Rule: corresponding dimension of the closest area ancestor that was generated by a block-level formatting object ===
I assume 'closest area ancestor that was generated by a block-level formatting object' is the same as
'closest ancestor block area that is not a line area'.
==== Properties ====
 * inline-progression-dimension

== 2.2 Rules referring to the 'parent area' ==
The difference to 'containing block' is that the 'parent area' could be a 'line area'
Therefore 'parent area' and 'containing block' may not be the same.
=== XSL-FO Rule: refer to inline-progression-dimension of content-rectangle of parent area ===
==== Properties ====
 * leader-length: Percentage support not implemented
 * leader-pattern-width: Percentage support not implemented

== 2.3 Rules referring to the containing reference area ==
=== XSL-FO Rule: refer to inline-progression-dimension of containing reference area ===
==== Properties ====
 * end-indent: Percentage support not configured
 * start-indent: Percentage support not configured

== 2.4 Rules refering to the area generated by the fo element itself ==
=== XSL-FO Rule: refer to size of padding-rectangle ===
==== Properties ====
 * background-position-horizontal
 * background-position-vertical

=== XSL-FO Rule: see prose ===
==== Properties ====
 * alignment-adjust: Percentage support not configured
   * XSL-FO: The computed value of the property is this percentage multiplied by the area's computed "height" if the area is generated by an fo:external-graphic or fo:instream-foreign-object, the "font-size" if the area was generated by an fo:character, and the "line-height" otherwise.

== 2.5 Rules related to tables ==
The only rule in this group refers the table width. It should be possible to obtain this through the
area tree. However, the actual percentage calculation is a fairly special case.
=== XSL-FO Rule: refer to width of table ===
==== Properties ====
 * column-width

= 3. Other rules not covered above =

== Rules refering to an elements intrinsic sizes ==
These apply to external-graphic and instream-foreign-object objects only.
They can be calculated the moment the intrinsic dimensions of the e-g or i-f-o are
known.
=== XSL-FO Rule: refer to intrinsic height ===
==== Properties ====
 * content-height

=== XSL-FO Rule: refer to intrinsic width ===
==== Properties ====
 * content-width

== Rules related to regions ==
=== XSL-FO Rule: refer to width of the region being divided into columns ===
The value is a percentage of the inline-progression-dimension of the 
content-rectangle of the region.
==== Properties ====
 * column-gap: Percentage support not configured

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