Make `symcal` work with lowercase latin letters

[marcin-serwin]

Status

READY

Description

The documentation describes mathcal and mathscr as synonyms, but the mathscr correctly maps the lowercase Latin letters, while mathcal only handles the uppercase letters. This PR changes the cal alphabet to be the same as scr.

Todo

• [x] Tests added to cover new/fixed functionality
• [x] Documentation added if necessary
• [x] Code follows expl3 style guidelines

Minimal example demonstrating the new/fixed functionality

\documentclass{article}
\usepackage{unicode-math}
\setmathfont{STIXTwoMath-Regular.otf}

\begin{document}
\[
    \symscr{ABCDabcd} \quad \symcal{ABCDabcd}
\]
\end{document}

Before

After

[wspr]

Sorry for the slow reply. I have no memory of why these were not defined identically to begin with! Many thanks for the initiative and the well organised pull request.