Rik Kabel via ntg-context schrieb am 26.09.2021 um 22:13:
>
> Hello list mavens,
>
> What are the circumstances under which style=italicface should be used 
> instead of style=italic. I note a difference when I define 
> highlighting. I expected to see no difference in the line before and 
> line after the hairline the example below, but see that italicface 
> adapts to nesting, while italic does not:
>
> Are there other places where this makes a difference?
>
>     \setupbodyfontenvironment
>             [default]
>             [em=italicface] %same with italic for this example
>     \definehighlight
>             [emIt]
>             [style=italic]
>     \definehighlight
>             [emIf]
>             [style=italicface]
>     \definehighlight
>             [emEm]
>             [style=\em]
>
>     \starttext
>
>     {\em abc {\em def} ghi}: \type{\em}
>
>     \emph{abc {\emph def} ghi}: \type{\emph}
>
>     \emEm{abc {\emEm def} ghi}: \type{\emEm \definehighlight[style=\em]}
>
>     \emIf{abc {\emIf def} ghi}: \type{\emIf
>     \definehighlight[style=italicface]}
>
>     \hairline
>
>     \emIt{abc {\emIt def} ghi}: \type{\emIt
>     \definehighlight[style=italic]}
>
>     \stoptext
>

The \em command has two special values which are allowed when you change 
the style with

     \setupbodyfontenvironment[default][em=...]

with the value "slanted" and "italic". When you choose one of them the 
result depends on the current weight (\tf or \bf) but with every other 
value you're just using whatever the style command/name provides.


When you pass "italicface" you're using a style which uses either \it or 
\bi dependant on the current weight. The result from the "italic" value 
doesn't depend on the behavior or the normal italic style (\it) which is 
the reason why you get different result when you use \em compared with \it.


Example:

\starttext

\tex{it}: normal {\it italic} {\bf bold {\it italic}}

\tex{italicface}: normal {\italicface italic} {\bf bold {\italicface 
italic}}

\tex{em}: normal {\em italic} {\bf bold {\em italic}}

\stoptext


Wolfgang