Simple table with caption:

\begin{longtable}[]{@{}rlcl@{}}
\caption{Demonstration of simple table syntax.}\tabularnewline
\toprule
Right & Left & Center & Default \\
\midrule
\endfirsthead
\toprule
Right & Left & Center & Default \\
\midrule
\endhead
12 & 12 & 12 & 12 \\
123 & 123 & 123 & 123 \\
1 & 1 & 1 & 1 \\
\bottomrule
\end{longtable}

Simple table without caption:

\begin{longtable}[]{@{}rlcl@{}}
\toprule
Right & Left & Center & Default \\
\midrule
\endhead
12 & 12 & 12 & 12 \\
123 & 123 & 123 & 123 \\
1 & 1 & 1 & 1 \\
\bottomrule
\end{longtable}

Simple table indented two spaces:

\begin{longtable}[]{@{}rlcl@{}}
\caption{Demonstration of simple table syntax.}\tabularnewline
\toprule
Right & Left & Center & Default \\
\midrule
\endfirsthead
\toprule
Right & Left & Center & Default \\
\midrule
\endhead
12 & 12 & 12 & 12 \\
123 & 123 & 123 & 123 \\
1 & 1 & 1 & 1 \\
\bottomrule
\end{longtable}

Multiline table with caption:

\begin{longtable}[]{@{}
  >{\centering\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.15}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.14}}
  >{\raggedleft\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.16}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.35}}@{}}
\caption{Here's the caption. It may span multiple lines.}\tabularnewline
\toprule
Centered Header & Left Aligned & Right Aligned & Default aligned \\
\midrule
\endfirsthead
\toprule
Centered Header & Left Aligned & Right Aligned & Default aligned \\
\midrule
\endhead
First & row & 12.0 & Example of a row that spans multiple lines. \\
Second & row & 5.0 & Here's another one. Note the blank line between rows. \\
\bottomrule
\end{longtable}

Multiline table without caption:

\begin{longtable}[]{@{}
  >{\centering\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.15}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.14}}
  >{\raggedleft\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.16}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.35}}@{}}
\toprule
Centered Header & Left Aligned & Right Aligned & Default aligned \\
\midrule
\endhead
First & row & 12.0 & Example of a row that spans multiple lines. \\
Second & row & 5.0 & Here's another one. Note the blank line between rows. \\
\bottomrule
\end{longtable}

Table without column headers:

\begin{longtable}[]{@{}rlcr@{}}
\toprule
\endhead
12 & 12 & 12 & 12 \\
123 & 123 & 123 & 123 \\
1 & 1 & 1 & 1 \\
\bottomrule
\end{longtable}

Multiline table without column headers:

\begin{longtable}[]{@{}
  >{\centering\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.15}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.14}}
  >{\raggedleft\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.16}}
  >{\raggedright\arraybackslash}p{(\columnwidth - 6\tabcolsep) * \real{0.35}}@{}}
\toprule
\endhead
First & row & 12.0 & Example of a row that spans multiple lines. \\
Second & row & 5.0 & Here's another one. Note the blank line between rows. \\
\bottomrule
\end{longtable}