[luatex] Default stretch, shrink values for tex.adjustspacing = 1

[Patrick Gundlach]

Hello all,

when I set tex.adjustspacing = 1, my documents seem to do some font expansion / shrinkage. Therefore I conclude that there might be some default values for font stretching and font shrinking.(*)

Question: what are the default values for stretching, shrinking and step when I set tex.adjustspacing to 1? 

Additional question: where can I find this in the LuaTeX code?

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This is LuaHBTeX, Version 1.15.0 (TeX Live 2022)
Development id: 7509
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and I run luatex --ini to avoid any external format interference.



(*) There might be the possibility that I set the values somewhere in my code and I cannot find it anymore. It might also be the case that I misinterpret my results. If possible, I would not have to make a MWE, but will do so if necessary.

Thank you

   Patrick