What does inhibiting leading does in (sub)section?

[Omikhleia]

Greetings,

The \section and \subsection in the (default) book class both do a SILE.typesetter:inhibitLeading() at their end. Chapters and parts do not.

I am trying to understand what it does, but couldn't make it out clearly. In my own class(es), I added it too to all my sectioning commands, but I am having weird behavior with it. It seems better looking without it, but I have no idea of the actual impact generally. What does it do exactly and when is it expected? Unless mistaken, it is only used there (i.e. section and subsection), so I assume there is a reason for it, but why only there then?

[alerque]

I believe this was an early way of setting \noindent, but these should be updated to actually use SILE.call("noindent") so we don't fragment the implementations. It should just avoid the next paragraph after section headings being indented.

[Omikhleia]

SILE.typesetter:inhibitLeading() bears no relation with SILE.call("noindent").
The former cancels vertical leading, the latter cancels paragraph indentation. Two different things for two different purposes.
This being said, the mystery why the book class cancels vertical leading after sections and subsections (only) remains entire ;)

[alerque]

Didier is right of course, I must have been sleep deprived back in Dec '21. Also @Omikhleia do we have a cross reference bug number for that?

[Omikhleia]

@alerque The closest related bug reference we have on that topic is #1300 (with Simon intervening on the difference between the vertical leading inhibition vs. the paragraph indent - but he didn't provide insights why the former was used in section and subsection)

[Omikhleia]

For those interested, Omikhleia/resilient.sile#27 - It's on a slightly different topic, but I also took that opportunity to show what inhibiting leading does (see the picture).

[Omikhleia]

Asking ChatGPT, "leading suppression" after header section is a matter of taste and typographic choice, without any strong rule or convention. I'll consider this is the answer.

As noted, in my own resilient.book class, I decided not to have this behavior.
As for SILE's default book class, I no longer use it, so let's say it may do it if it so wishes - whatever occurs then with other layout strategies (grid, etc.) is beyond the initial question I had in 2021.