I am going to think out loud about the line area layout process.

This is partly implemented and I want to document some of the problems and 
thinking involved.

The block area firstly gets all of the layout managers from its children. 
Then it combines consecutive inline area layout managers and converts into 
a single line layout manager. All inline layout managers have no children. 
This means that nested inline elements are flattened into a list of inline 
area layout managers.

When flattening the parent inline level sets start and end properties on 
the layout managers.
The line layout manager gets an inline area from the child layout managers 
using an index. This means it is easy to keep track of and to backtrack.

The problems:
initial property set
These properties need to become the parent property set of the inline 
areas created in the first line of a block.

an inline area could have a keep with next or previous or an implicit keep 
between characters.

areas resolved depending on page
page reference numbers must be resolved depending on the current page

changing inline progression dimension
adding side floats could change to available inline progression dimension

stretchable areas
areas such as space, leader may stretch to fill space towards optimum value

properties over a range of areas
properties such as id area, link, background can only be set over a range, 
it is not sensible to set on every inline area

this needs to be determined independantly from the inline area layout 
managers since different managers may return consecutive characters

The solution:
The initial property set is given to the inline layout managers if this is 
the first line, areas that didn't make it are re-retrieved without the 
property set.
Temporary data is set on every inline area, this data also tells us of any 
keeps. When adding children we add the current area and have the next area 
for reference.
The best break is stored with the current position and min/opt/max length. 
Inlines areas are added until no more can possibly fit.
The areas are always retrieved from the inline layout managers, they are 
only stored in completed line areas. If a line area needs to change ipd 
then we start from the beginning. Line areas that contain resolved values 
also are re-retrieved.
Stretching areas is a bit tricky. Spaces are stretched by the user agent 
and leader and others can have a range. This process is done after the 
inline areas have been completed for the line.
Things like side floats, before floats, footnotes, range properties are 
retrieved from the child layout managers before/after getting the inline 
areas. These areas remain linked to a line so that removing the line will 
allow us to remove the float or footnote.
Hyphenation is a bit difficult, having hyphenation on a single character 
complicates the matter. If it is hyphenating then we need to combine all 
consecutive character areas regardless of properties and apply the 

The index used to get inline areas can also be used to free memory when a 
page is completed.

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