Re: e-g with padding and borders

[Luca Furini]

Manuel Mall wrote:

Next problem: border conditionality - how do I model that with the Knuth 
approach? At the time I add the Border/Padding start/end boxes we don't 
have line breaks so they really only cover the .conditionality=discard 
case. How do I tell the algorithm to leave enough space at the end of 
each line (and the beginning of the next line) for the borders (in the 
case of .conditionality=retain)?

The sequence of elements representing the inline content starts and ends 
with a box [1].

Adding another box at the beginning and at the end of the sequence 
implements "retain", as a line break is never allowed to separate two 
adjacent boxes: so, the left border and padding will always be in same 
line as the first piece of content, and the breaking algorithm will always 
reserve enough space.

In order to implement "discard", glue elements must be used instead: these 
elements are discarded if they are chosen as a line break or they are 
adjacent to a line break, and in this case borders and padding will not be 
painted.

I think that a single box or glue element could be created, representing 
both border and padding, unless the conditionalities of these properties 
can be different: for example, if it were possible to have 
border-start.conditionality = "discard" and padding-start.conditionality = 
"retain" two distinct elements should necessarily be created.

Regards
    Luca

[1] Or, better, everything should work well if the first and last elements 
are boxes. Should there be spaces at the beginning and at the end of the 
inline having borders, they should be handled as non-breaking spaces, in 
order to avoid a break between the start border and the first word, or 
between the last word and the end border.