[NTG-context] fullhz, kerning and glue

[Henning Hraban Ramm]

Hi,
I just added an explanation of "fullhz" to the options in 
https://wiki.contextgarden.net/Command/setupalign.
but I’m actually unsure if it’s right.

In the sources I found:
https://source.contextgarden.net/tex/context/base/mkxl/hand-ini.mkxl

%D At some point we can introduce extreme expansion, i.e. \type 
{\normaladjustspacing\plustwo}.
56
57% 0 = disabled
58% 1 = notused      (thesis)
59% 2 = glyph + kern
60% 3 = glyph only   (default)
61
62\def\font_expansion_enable  {\normaladjustspacing\plusthree}
63\def\font_expansion_enable_k{\normaladjustspacing\plustwo}
64%def\font_expansion_enable_n{\normaladjustspacing\plusone}
65\def\font_expansion_disable {\normaladjustspacing\zerocount}

And "fullhz" in spac-ali.mkxl calls \font_expansion_enable_k.

So, apparently fullhz enables stretching of *kerning* – that sounds to 
me like letterspacing.

OTOH in my notes (and thus in my book) I have the information that 
fullhz enables stretching of *glue*, and I thought that would mean 
whitespace outside of words.

Please enlighten me?

Hraban