How to define new horizontal alignment in tabularray - TeX

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How to define new horizontal alignment in tabularray

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samcarter

While looking for a workaround for [CarLaTeX's recent question](https://topanswers.xyz/tex?q=2217) I was wondering if it is possible for a user to define a new horizontal alignment in tabularray. 

My naive attempt was to look into the source for  `\TblrAlignRight`, copy these lines and and give them a new name:

```
\documentclass{article} 

\usepackage{tabularray}

\NewDocumentCommand\TblrAlignSam{}{\raggedleft}

\ExplSyntaxOn
\cs_new_eq:NN \__tblr_halign_command_s: \TblrAlignSam
\ExplSyntaxOff

\begin{document}
\begin{tblr}{colspec={Q[s,t]Q[c,m]Q[l,b]}, hlines}
{The baseline is\\ at the top\\ (right aligned)} & 
{The baseline is\\ in the middle\\ (centered)} & 
{The baseline is\\ at the bottom\\ (left aligned)}\\ 
\end{tblr}
\end{document}
```

However this results in the error

```
! Undefined control sequence.
<argument> \color 
                  {\l__tblr_b_tl }\vrule width \dim_use:N \l_tmpa_dim  heigh...
l.16 \end
         {tblr}
```

Is there a way for an user to define additional horizontal alignments?

Top Answer

samcarter

Rubber duck debugging worked great and as soon as I posted the question, I found a solution :)

I also need to add it to the tblr-column keys:

```
\documentclass{article} 

\usepackage{tabularray}

\NewDocumentCommand\TblrAlignSam{}{\raggedleft}

\ExplSyntaxOn
\cs_new_eq:NN \__tblr_halign_command_s: \TblrAlignSam
\keys_define:nn { tblr-column } { s.meta:n = { halign = s } }
\ExplSyntaxOff

\begin{document}
\begin{tblr}{colspec={Q[s,t]Q[c,m]Q[l,b]}, hlines}
{The baseline is\\ at the top\\ (right aligned)} & 
{The baseline is\\ in the middle\\ (centered)} & 
{The baseline is\\ at the bottom\\ (left aligned)}\\ 
\end{tblr}
\end{document}
```

Or alternatively explicitly use `halign=s` in the column instead of the shorthand:

```
\documentclass{article} 

\usepackage{tabularray}

\NewDocumentCommand\TblrAlignSam{}{\raggedleft}

\ExplSyntaxOn
\cs_new_eq:NN \__tblr_halign_command_s: \TblrAlignSam
\ExplSyntaxOff

\begin{document}
\begin{tblr}{colspec={Q[halign=s,t]Q[c,m]Q[l,b]}, hlines}
{The baseline is\\ at the top\\ (right aligned)} & 
{The baseline is\\ in the middle\\ (centered)} & 
{The baseline is\\ at the bottom\\ (left aligned)}\\ 
\end{tblr}
\end{document}
```

1 Answer