I have seen Table with 100 % width and vertical / horizontal alignment, Vertically center text in tabularx table, Vertical alignment in tabularx X column type - and I'm trying what they suggest, but it doesn't work.
Consider this MWE:
\documentclass{article}
\usepackage{array,booktabs}
\usepackage{tabularx}
\usepackage{ragged2e}
\usepackage{hhline}
\newcolumntype{x}[1]
{>{\raggedright}p{#1}}
\newcolumntype{z}[1]
{>{\centering}p{#1}}
\newcommand{\tn}{\tabularnewline}
\renewcommand\tabularxcolumn[1]{>{\Centering}m{#1}} %% COMMENT
\begin{document}
\begin{table}[!h]%t1
\caption{A rather long explanation of what this table is supposed to be}
\small%
{%
\begin{tabularx}{\textwidth}%
{|x{2.6cm}|X|} %% COMMENT
% {|x{2.6cm}|>{\centering}X|} %% UNCOMMENT
\hline
Something something & something else \tn
\hhline{|=|=|}
\textbf{Item one} \\ {\small\it item ref 1} &%
param 01 / param 02 \\/ param3\tn
\hline
\textbf{Item two} \\ {\small\it item ref 2} &%
param 03 / param 04 \\/ param5\tn
\hline
\textbf{Item two} \\ {\small\it item ref 2} &%
param 03 / param 04 / param5\tn
\hline
\end{tabularx}}
\label{tab:sometable}
\end{table}
\end{document}
As is, this produces:

... so clearly something is broken (the \\ are seen as new table lines, I guess)?
But if you uncomment/comment the lines as marked with %% in the MWE, it compiles almost fine:

... except there is no vertical centering - as evidenced by the 3rd row, 2nd column.
So how can I have a column that stretches, that allows line breaking inside a cell - and centers the text vertically?

xto\newcolumntype{x}[1]{>{\raggedright}m{#1}}to get the cells vertically centered. – esdd May 10 '15 at 20:00\makeatletter, I finally get vertically centered columns (img2). Thanks again both - cheers! – sdaau May 10 '15 at 20:09\raisebox{-0.5em}{text}etc manually wrapping a cell's content, if there are just a few cells to adjust vertically, without having to loadragged2e(or redefine columns for vertical centering). – sdaau May 10 '15 at 20:22|themcolumn was centering the second column, so aligning its centre with the reference point of the cell in first column (its first line), usingmin both puts the reference points of both cells in their centre. – David Carlisle May 10 '15 at 20:22\newcolumntype{x}...causesPackage array Warning: Column x is already defined). Cheers! – sdaau May 10 '15 at 20:24xtwice. It does not by default or in this MWE – David Carlisle May 10 '15 at 20:26