\tl_new:N \__text
\mmmmxxxv_define_fp_var:Nn{\Total}{0}
\seq_map_inline:Nn \l_mmmmxxxv_fp_seq
 {
   %here I don't understand, how to check that we are processing the last
   %element of sequence and don't put '+'
   \tl_put_right:Nx \__text {\getfpvar{#1} +}
   \fp_add:Nn \Total #1
 }
\show\__text

% since \seq_use:cnnn doesn't exist, we create it
\cs_generate_variant:Nn \seq_use:Nnnn { c }

\cs_generate_variant:Nn \seq_use:Nnnn { cnnn }

This answer is correct tex.stackexchange.com/questions/12773/or-left-parentheses  I did not notice there is an extra space when comparing

$H(s)$

 $H\left(s\right)$

until I zoomed in the PDF

\documentclass{article}
\usepackage{expl3}
\begin{document}
\ExplSyntaxOn

\cs_generate_variant:Nn \skip_split_finite_else_action:nnNN { N }

\skip_gset:Nn \g_tmpa_skip { 2pt~plus~.4pt~minus~.3pt  }
\skip_split_finite_else_action:nnNN \g_tmpa_skip {  } \g_tmpa_dim \g_tmpb_dim



\begin{tabular}{ll}
	Skip~orig:           & \skip_use:N \g_tmpa_skip \\
	stretch~component:   & \dim_use:N \g_tmpa_dim   \\
	shrink~component:    & \dim_use:N \g_tmpb_dim   \\
	Skip~without~strech: &
	\skip_gset:Nn \g_tmpb_skip { \g_tmpa_skip - 0pt~plus~\g_tmpa_dim~minus~\g_tmpb_dim }

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{lindenmayersystems}

\begin{document}
\begin{tikzpicture}[l-system={step=5pt, order=5, angle=120}]
\pgfdeclarelindenmayersystem{Sierpinski triangle}{
\symbol{X}{\pgflsystemdrawforward}
\symbol{Y}{\pgflsystemdrawforward}
\rule{X -> X-Y+X+Y-X}
\rule{Y -> YY}
}
\draw [blue] (3,2) l-system
[l-system={Sierpinski triangle, axiom=X, anchor=north east}];
\end{tikzpicture}

\end{document}

import binascii
binascii.unhexlify(b'6365726564614075736572732e73662e6e6574')

"6365726564614075736572732e73662e6e6574".decode("hex")

And the quote show up stright UP fine in PDF since I am using this:

\usepackage{fancyvrb}
\usepackage{upquote,textcomp}

in HTML like this:
<PRE>
 'test'
</PRE>
it looks just fine :(