[luatex] prev field in discretionary nodes

[Taco Hoekwater]

Hi,

On 18 Jan 2014, at 10:41, Stephan Hennig <mailing_list at arcor.de> wrote:

> Hi,
> 
> below you can find a textual representation of the discretionary node
> resulting from the command \discretionary{a-}{b}{c}.  Lines beginning
> with a + sign contain additional information to the preceding line.
> 
> nl: <node    199 <    208 >    236 : disc 0>
> nl: +pre:
> nl:   <node    212 <    181 >    218 : glyph 1>
> nl:   +char: a
> nl:   <node    181 <    218 >    nil : glyph 1>
> nl:   +char: -
> nl: +post:
> nl:   <node    214 <    224 >    nil : glyph 1>
> nl:   +char: b
> nl: +replace:
> nl:   <node    216 <    230 >    nil : glyph 1>
> nl:   +char: c
> 
> In this example, one can see that nodes 181, 224, 230 (first nodes in
> sub-lists) do have a prev field set.  But that points neither to the
> discretionary node (208) nor to any preceding node in the node list (not
> shown here).

> What do the first prev fields in pre, post, replace sub-lists of
> discretionary nodes point to?
> 

214, 216, and 218 are the field headers of the various lists inside
the discretionary node (the pre,post,replace fields). It is a bit of a trick
that helps the discretionary replacement code in the paragraph builder.

Best wishes,
Taco