Change default column type in tabularray

Question

Is it possible to set all tblr in the document to be \linewidth wide specifying the X column type by default?. This requires not mentioning the number of columns like it happens in colspec, as it varies for every tblr.

In this case, colspec could be used in certain columns where the default column type should be overriden.

For instance:

\documentclass{article}
\usepackage{tabularray}

\setlength{\parindent}{0mm}

% act here to specify a default column type

\SetTblrInner{
 width=\linewidth,
 %columns={X},
 baseline=T,
 hspan=even,
 vspan=even,
 stretch=1.3,
 row{1}={font=\bfseries},
 hline{1,Z}={0.6mm},
 hline{2}={0.3mm}
}

\begin{document}

 These tables should all have the same width without further modifications in the document body

 \begin{table}[!hb]
  \begin{tblr}{colspec={XX}}
   Head1 & Head2 \\
   Row21 & Row22 \\
   Row31 & Row32 \\
  \end{tblr}

  \begin{tblr}{}
   Head1 & Head2 \\
   Row21 & Row22Row22 \\
   Row31 & Row32 \\
  \end{tblr}

  \begin{tblr}{}
   Head1 & Head2 & Head3\\
   Row21 & Row22 & Row23 \\
   Row31 & Row32 & Row33 \\
   Row41 & Row42 & Row43 \\
  \end{tblr}

  \begin{tblr}{colspec={|l|X[r]|c|}}
   Head1 & Head2 & Head3\\
   Row21 & Row22 & Row23 \\
   Row31 & Row32 & Row33 \\
   Row41Row41 & Row42 & Row43 \\
  \end{tblr}
 \end{table}
\end{document}

Answer 1

You've found the right option, columns. The last step is to feed it a column key-value list, like co=1,bg=blue!20, not an other column type like X.

By uncommenting the columns={X}, line in OP's example and replacing it with columns={co=1},, you'll get

\documentclass{article}
\usepackage{tabularray}

\setlength{\parindent}{0mm}

% act here to specify a default column type

\SetTblrInner{
 width=\linewidth,
 columns={co=1},
 baseline=T,
 hspan=even,
 vspan=even,
 stretch=1.3,
 row{1}={font=\bfseries},
 hline{1,Z}={0.6mm},
 hline{2}={0.3mm}
}

\begin{document}

 These tables should all have the same width without further modifications in the document body

 \begin{table}[!hb]
  \begin{tblr}{colspec={XX}}
   Head1 & Head2 \\
   Row21 & Row22 \\
   Row31 & Row32 \\
  \end{tblr}

  \begin{tblr}{}
   Head1 & Head2 \\
   Row21 & Row22Row22 \\
   Row31 & Row32 \\
  \end{tblr}

  \begin{tblr}{}
   Head1 & Head2 & Head3\\
   Row21 & Row22 & Row23 \\
   Row31 & Row32 & Row33 \\
   Row41 & Row42 & Row43 \\
  \end{tblr}

  \begin{tblr}{colspec={|l|X[r]|c|}}
   Head1 & Head2 & Head3\\
   Row21 & Row22 & Row23 \\
   Row31 & Row32 & Row33 \\
   Row41Row41 & Row42 & Row43 \\
  \end{tblr}
 \end{table}
\end{document}

Update

Unfortunately, because column types like l and c only set halign (to l and c, respectively) and don't reset co to its initial value 0 (which is altered by previous columns={co=1}), after setting columns={co=1}, a table with colspec={|l|X[r]|c|} will work like

colspec={|Q[l,co=1]|Q[r,co=1]|Q[c,co=1]|}

while what user may expect is

colspec={|Q[l,co=0]|Q[r,co=1]|Q[c,co=0]|}

One workaround is to explicitly use colspec={|Q[l,co=0]|X[r]|Q[c,co=0]|}. (Currently there's no public interface to redefine an existing row/column type and column types setting horizontal alignment like l and c don't have an optional argument.)

Reported to tabularray, see https://github.com/lvjr/tabularray/issues/411.

\documentclass{article}
\usepackage{tabularray}

\setlength{\parindent}{0mm}

% act here to specify a default column type

\SetTblrInner{
 width=\linewidth,
 columns={co=1},
 baseline=T,
 hspan=even,
 vspan=even,
 stretch=1.3,
 row{1}={font=\bfseries},
 hline{1,Z}={0.6mm},
 hline{2}={0.3mm}
}

\def\testTblrColspec#1{
  \hspace*{-2em}\texttt{\UseName{tl_if_empty:nTF}{#1}{<empty>}{#1}}
  \par\medskip
  \begin{tblr}{#1}
   Head1 & Head2 & Head3\\
   Row21 & Row22 & Row23 \\
   Row31 & Row32 & Row33 \\
   Row41Row41 & Row42 & Row43 \\
  \end{tblr}
  \par\medskip
}

\begin{document}

\testTblrColspec{}
\testTblrColspec{colspec={|l|X[r]|c|}}
\testTblrColspec{colspec={|Q[l,co=0]|X[r]|Q[c,co=0]|}}

\end{document}