Using foreach to add variable number of rows to a bytefield inside a TikZ node?

Question

I'd like to loop over a list of fields to be added to a bytefield, to be shown inside a TikZ node. MWE:

\documentclass[tikz]{standalone}

\usepackage{bytefield}
\usepackage{etoolbox}

\begin{document}

% inspired by : https://tex.stackexchange.com/questions/654504/using-foreach-to-add-rows-containing-references-to-pgfplots-objects-in-a-matrix

\begin{tikzpicture}
  \node {
    \begin{bytefield}{8}
      \wordbox{1}{Source: A} \\
      \makeatletter
      \let\@gtempa\@empty 
      \foreach \f in {1,2,3} { \xappto\@gtempa{\noexpand\wordbox{1}{Field: \f}\noexpand\\}}
      \@gtempa
      \makeatother 
    \end{bytefield}
  };
\end{tikzpicture}
\end{document}

Idea is based on Using \foreach to add rows containing references to pgfplots objects in a matrix of nodes

It almost works, but the first field is indented:

How to get rid of that indentation??

What I REALLY want to do is to loop over a list of nodes with variable number of fields and to construct byte fields dynamically. Something like below (of course, this is simplified, just to get the idea across).

% What I REALLY want to do; just a sketch; this fails  
\begin{tikzpicture}

  \node [draw] (a) {a};
  \node [draw] at (6,0) (b) {b};

  \foreach \n/\fields in {a/{1,2,3},b/{4,5}} {
    \node [below=of \n] { 
      \begin{bytefield}{8}
        \wordbox{1}{Source: \n} \\
        \wordbox{1}{\fields} \\
        % This sort of works, but not what I want: 
        \wordbox{1}{\foreach \f in \fields {\f ; } }
        % What I really want, but fails with Missing \endgroup inserted.: 
        % \foreach \f in \fields {
        % \wordbox{1}{\f} \\
        % }
      \end{bytefield}
    };
  }
  
\end{tikzpicture}

Answer 1

Just use the /.list handler.

\documentclass[tikz]{standalone}

\usepackage{bytefield}

\begin{document}

\begin{tikzpicture}[wordbox/.code={\\\wordbox{1}{Field: #1}}]
  \node {
    \begin{bytefield}{8}
      \wordbox{1}{Source: A} 
      \tikzset{wordbox/.list={1,2,3}}
    \end{bytefield}
  };
\end{tikzpicture}
\end{document}