Combine si and font ignores font suggestion

[Aljumaily]

It seems that combining si={...} and font=... ignores the font suggestion. The output in the "Expected" column is the desired output.

\documentclass{article}
\usepackage[margin=1in]{geometry}
\usepackage{xcolor}
\usepackage{tabularray}
\UseTblrLibrary{siunitx}

\begin{document}

\begin{tblr}{
    hlines, vlines,
    column{1}={si={table-format=2.3, round-mode=places, round-precision=3}},
    column{2}={font=\itshape},
    column{3}={ % unexpected behaviour
        si={table-format=2.3, round-mode=places, round-precision=3},
    font=\itshape
    },
    column{4}={font=\itshape},
    row{1}={guard, font=\normalfont\bfseries}
  }
    Formatted & Font changed & Formatted \& Font changed & Expected \\
    10.1      & 10.1         & 10.1                      & 10.100   \\
    20.2      & 20.2         & 20.2                      & 20.200   \\
    30.3      & 30.3         & 30.3                      & 30.300   \\
    40.4      & 40.4         & 40.4                      & 40.400   \\
\end{tblr}
\end{document}

[muzimuzhi]

si={...} won't ignore font key, for example si={...}, font=\Large does affect the font size. It is siunitx that ignores \itshape.

By default siunitx prints output in math mode, and even when configured to print in text mode, by default it uses a static \upshape\mdseries\rmfamily font setting. See siunitx package doc (2023-08-03), sec. 4.2 "Printing" for more info.

In example below, siunitx configuration mode=match, reset-text-shape=false is added to print output in text mode if the input is in text mode and allow font shape switching. To be complete, you may also want to set reset-text-family=false, reset-text-series=false.

\documentclass{article}
\usepackage{tabularray}
\usepackage{xcolor}
\UseTblrLibrary{siunitx}

\begin{document}

{
  \sisetup{round-mode=places, round-precision=3}
  \itshape

  % \sisetup{mode=math, reset-text-shape=true} % default setting
  \num{10.1} in text mode, $\num{10.2}$ in math mode\par

  \sisetup{mode=match} % no effect
  \num{10.1} in text mode, $\num{10.2}$ in math mode\par

  \sisetup{mode=match, reset-text-shape=false} % now works, in text mode number is in italic
  \num{10.1} in text mode, $\num{10.2}$ in math mode\par
}

\begin{tblr}{
    hlines, vlines,
    column{1}={si={table-format=2.3, round-mode=places, round-precision=3}},
    column{2}={font=\itshape},
    column{3}={
        si={table-format=2.3, round-mode=places, round-precision=3, mode=match, text-font-command=\itshape},
        font=\itshape
    },
    column{4}={font=\itshape},
    row{1}={guard, font=\normalfont\bfseries}
  }
    Formatted & Font changed & Formatted \& Font changed & Expected \\
    10.1      & 10.1         & 10.1                      & 10.100   \\
    20.2      & 20.2         & 20.2                      & 20.200   \\
    30.3      & 30.3         & 30.3                      & 30.300   \\
    40.4      & 40.4         & 40.4                      & 40.400   \\
\end{tblr}
\end{document}

[Aljumaily]

@muzimuzhi Thank you for the perfect and detailed response!