\[
% Defines an openable reference to the given tag
\newcommand\fref[2][]{
\hspace{1em}
\cssId{ref#1:#2}{
\class{start-socket}{
\phantom{\Box}
}
}
}
% Defines an inline reference to the given tag
\newcommand\ifref[2][]{
\cssId{ref#1:#2}{
\class{start-socket}{
\phantom{}
}
}
}
% Defines a tag to reference later
\newcommand\ftag[1]{
\cssId{tag:#1}{
\class{end-socket}{
\phantom{\large #1\Box}
}
}
}
\]