Verbatim

<..fix fancyvrb..>
 \pend:def\FV@FormattingPrep{<.find color for fancyvrb.>}
 \append:def\FV@FormattingPrep{\a:fancyvrb
    <.frames for fancyvrb.>%
    <.color for fancyvrb.>%
 }
 -_-_-

\FV@RightListNumber not recognized in ttct.cls with test.tex. Why?

<..fix fancyvrb..>+
 \def\FV@ListProcessLine#1{%
     \hbox{\c:fancyvrb \anc:lbl r{FancyVerbLine}\FV@LeftListNumber
       \FV@LeftListFrame \e:fancyvrb \FancyVerbFormatLine{#1}\f:fancyvrb
       \FV@RightListFrame \csname FV@RightListNumber\endcsname
           \d:fancyvrb}}
 \def\FV@EndList{\FV@ListProcessLastLine  \FV@EndListFrame
   \IgnorePar\b:fancyvrb\par\@endparenv
   \endgroup   \@endpetrue}
 \def\FV@StepLineNo{%
   \FV@SetLineNo
   \def\FV@StepLineNo{\SkipRefstepAnchor\refstepcounter{FancyVerbLine}}%
   \FV@StepLineNo}
 -_-_-

The command \@endparenv will complain if encounter in horizontal mode.

‘\Configure{fancyvrb} {before-env} {after-env} {before-line} {after-line} {before-text} {after-text}’—beween end points of lines, and of tex, we can have line numbers.

<..fancyvrb.sty shared config..>
 \NewConfigure{fancyvrb}{6}
 -_-_-