\documentclass{report}
\usepackage{hyperref}
% WARNING: THIS SHOULD BE MODIFIED DEPENDING ON THE LETTER/A4 SIZE
\oddsidemargin 0cm
\evensidemargin 0cm
\marginparsep 0cm
\marginparwidth 0cm
\parindent 0cm
\textwidth 16.5cm

\ifpdf
  \usepackage[pdftex]{graphicx}
\else
  \usepackage[dvips]{graphicx}
\fi

% definitons for warning and note tag
\usepackage[most]{tcolorbox}
\newtcolorbox{tcbwarning}{
 breakable,
 enhanced jigsaw,
 top=0pt,
 bottom=0pt,
 titlerule=0pt,
 bottomtitle=0pt,
 rightrule=0pt,
 toprule=0pt,
 bottomrule=0pt,
 colback=white,
 arc=0pt,
 outer arc=0pt,
 title style={white},
 fonttitle=\color{black}\bfseries,
 left=8pt,
 colframe=red,
 title={Warning:},
}
\newtcolorbox{tcbnote}{
 breakable,
 enhanced jigsaw,
 top=0pt,
 bottom=0pt,
 titlerule=0pt,
 bottomtitle=0pt,
 rightrule=0pt,
 toprule=0pt,
 bottomrule=0pt,
 colback=white,
 arc=0pt,
 outer arc=0pt,
 title style={white},
 fonttitle=\color{black}\bfseries,
 left=8pt,
 colframe=yellow,
 title={Note:},
}

\begin{document}
% special variable used for calculating some widths.
\newlength{\tmplength}
\chapter{Unit ok{\_}lists}
\section{Description}
Test of lists tags.\hfill\vspace*{1ex}



Normal lists: \begin{enumerate}
\setcounter{enumi}{0} \setcounter{enumii}{0} \setcounter{enumiii}{0} \setcounter{enumiv}{0} 
\item One
\setcounter{enumi}{1} \setcounter{enumii}{1} \setcounter{enumiii}{1} \setcounter{enumiv}{1} 
\item Two
\setcounter{enumi}{2} \setcounter{enumii}{2} \setcounter{enumiii}{2} \setcounter{enumiv}{2} 
\item Three
\end{enumerate} \begin{itemize}
\item One
\item Two
\item Three
\end{itemize}

Empty list is accceptable:  

Whitespace inside lists is acceptable (and empty line that is not inside any @item is \textit{not} a paragraph): \begin{enumerate}
\setcounter{enumi}{0} \setcounter{enumii}{0} \setcounter{enumiii}{0} \setcounter{enumiv}{0} 
\item One
\setcounter{enumi}{1} \setcounter{enumii}{1} \setcounter{enumiii}{1} \setcounter{enumiv}{1} 
\item Two
\setcounter{enumi}{2} \setcounter{enumii}{2} \setcounter{enumiii}{2} \setcounter{enumiv}{2} 
\item  Other tags inside the items are allowed, e.g. \begin{ttfamily}link to self\end{ttfamily}(\ref{ok_lists}), \begin{ttfamily}True\end{ttfamily}, \texttt{}\textbf{begin}\texttt{~X~:=~Y;~}\textbf{end}\texttt{;\\
}, \textbf{something bold}, URLs: http://pasdoc.sf.net/, paragraphs:

2nd paragraph, dashes: em dash ---, en dash --, short one {-}, two consecutive short dashes {-}{-}. 
\end{enumerate}

Nested lists are also freely allowed: \begin{enumerate}
\setcounter{enumi}{0} \setcounter{enumii}{0} \setcounter{enumiii}{0} \setcounter{enumiv}{0} 
\item  1st nested unordered list: \begin{itemize}
\item One
\item Two
\item Three
\end{itemize} 
\setcounter{enumi}{1} \setcounter{enumii}{1} \setcounter{enumiii}{1} \setcounter{enumiv}{1} 
\item  2nd nested unordered list: \begin{itemize}
\item One
\item Two
\item Three
\end{itemize} 
\setcounter{enumi}{2} \setcounter{enumii}{2} \setcounter{enumiii}{2} \setcounter{enumiv}{2} 
\item  And a couple of single{-}item ordered lists nested: \begin{enumerate}
\setcounter{enumi}{0} \setcounter{enumii}{0} \setcounter{enumiii}{0} \setcounter{enumiv}{0} 
\item  \begin{enumerate}
\setcounter{enumi}{0} \setcounter{enumii}{0} \setcounter{enumiii}{0} \setcounter{enumiv}{0} 
\item  
\end{enumerate}
\end{enumerate}

(Source code of this example begins to look like LISP :) 
\end{enumerate}

Definition lists tests:

\begin{description}
\item[] 1st item
\item[] 2nd item
\end{description}

\begin{description}
\item[1st item label] 1st item
\item[2nd item label] 2nd item
\end{description}

\begin{description}
\item[1st item label] 
\item[2nd item label] 
\end{description}

Item spacing tests:

\begin{description}
\item[1st item label] 1st item
\item[2nd item label] 2nd item
\end{description}

\begin{enumerate}
\setcounter{enumi}{0} \setcounter{enumii}{0} \setcounter{enumiii}{0} \setcounter{enumiv}{0} 
\item One
\setcounter{enumi}{1} \setcounter{enumii}{1} \setcounter{enumiii}{1} \setcounter{enumiv}{1} 
\item Two
\setcounter{enumi}{2} \setcounter{enumii}{2} \setcounter{enumiii}{2} \setcounter{enumiv}{2} 
\item Three
\end{enumerate}
\end{document}
