You can also specify more than one underline setting, and Halibut
will choose the first one that the output character set supports.
So, for example, you could write
-\cw{\\text-chapter-underline\{\u203e\}\{\-\}}, and Halibut would use
+\cw{\\text-chapter-underline\{\\u203e\}\{\-\}}, and Halibut would use
the Unicode \q{OVERLINE} character where possible and fall back to
the ASCII minus sign otherwise.