selnolig-package and round s (s:) in fraktur (yfonts)

Question

In a German document I would like to typeset some selected phrases in Fraktur while the rest is written in Linux Libertine. Using the yfonts-package, the round s (the 'modern' one as opposed to the tall s) is achieved with the input s:.

The first MWE:

\documentclass[border=2]{standalone}

\usepackage{libertine}
\usepackage{yfonts}
\usepackage[ngerman]{babel} 

\begin{document}
    \frakfamily
    The quick fox jumps: over the sleazy dog
\end{document}

results in:

However, it appears that the selnolig-package (used in my document for the non-Fraktur text) prevents this output:

\documentclass[border=2]{standalone}

\usepackage{libertine}
\usepackage{yfonts}
\usepackage[ngerman]{babel} 
\usepackage[ngerman]{selnolig}

\begin{document}
    \frakfamily
    The quick fox jumps: over the sleazy dog
\end{document}

results in:

Is there a way to disable the selnolig-package for this particular case?

Answer 1

You can define your own macros and bypass the predefined ligature automation.

Apart from the round s, you should perhaps also define macros for the most basic macros that should be used in typographically correctly typeset Fraktur, namely ch, ck and tz (as can be seen from your example, these are also broken by selnolig):

\documentclass[border=2]{standalone}

\usepackage{libertine}
\usepackage{yfonts}
\usepackage[ngerman]{babel} 
\usepackage[ngerman]{selnolig}

\DeclareTextSymbol{\ch}{LY}{133}
\DeclareTextSymbol{\ck}{LY}{134}
\DeclareTextSymbol{\tz}{LY}{139}
\DeclareTextSymbol{\rounds}{LY}{141}

\begin{document}
    \frakfamily
    The qui\ck{} fox jump\rounds{} bli\tz{}s\ch{}nell over the sleazy dog
\end{document}

Answer 2

I will confess to having no knowledge of how the yfonts package goes about doing its work of converting s: to a Fraktur round-s. However, I gather that the package implements the conversion of s: to round-s as a ligature (in the TeX sense of the word). For sure, I can't think of any other reason for why selnolig -- which, after all, exists to suppress ligatures -- would interfere with the conversion of s: to round-s.

What I find truly baffling is that this inference occurs at all. For sure, if the selnolig package is loaded with the option ngerman, absolutely no \nolig directives are set up to suppress the s: ligature, either selectively or globally.

All I can suggest for now is that you run \selnoligoff to -- you guessed it -- switch off the operations of selnolig's routines before running \frakfamily. To reactivate selnolig's routines once you're back main document family, run \selnoligon.

E.g., something like the following:

\selnoligoff {\frakfamily 
The quick brown fox jumps: over the lazy dog.
}

\selnoligon
auffallen aufisst aufjaulen % suppress ff, fi, and fj ligatures

Because selnolig's routines don't recognize (and therefore ignore) TeX groups, be sure to let a paragraph break occur before executing \selnoligon. This works because selnolig's routines modify TeX's paragraph builder processes. Hence,

{\frakfamily 
The quick brown fox jumps: over the lazy dog.
} \selnoligoff 

auffallen aufisst aufjaulen
\selnoligon

will also get the job done, as \selnoligoff and \selnoligon kick in before the respective paragraph break occur. I agree that this must look downright weird to an old TeX hand.

I realize that this work-around isn't exactly elegant. And it might be quite tedious to implement if the document has lots of instances of \frakfamily.