Remember coordinate in nested tikzpicture points to a weird place

Question

I have problems with remembering the coordinates of names defined in nested tikz pictures. Look at the following minimal working example:

\documentclass{article}
\usepackage{tikz-qtree}
\newcommand{\inlinenode}[2]{
There are\\
several line\\
breaks\\
#2\tikz[remember picture]\coordinate (#1);\\
and #1 is not\\
in the center}
\begin{document}
\tikzset{every tree node/.style={align=center,anchor=north}}
\begin{tikzpicture}
\Tree [.{Root}
        [.\node{\inlinenode{x1}{$x_1$}}; ]
        [.\node (x2) {$x_2$}; ]
      ]
\path[thick,color=red] (x1) edge (x2);
\end{tikzpicture}
\end{document}

I want to connect x1 with x2 using the red line, which works fine for x2, but the other end is pointing in a weird place instead of to x1.

I have tried running pdflatex multiple times, but then the position of x1 gets even weirder.

What I want to achieve should be visible in the picture above, I want a multiline node with a special word/graphic inside the text and then connecting this word to another node (or even another special word inside another multiline text of a node). Feel free to modify my approach.

I also tried replacing the #2\tikz...\coordinate(#1) with \subnode{#1}{#2} (as in this similar question), but this has the same result.

Answer 1

In tikz-qtree, each child is actually a separate pgfpicture. This means that when drawing between children in the way that you do, you are drawing between two different pgfpictures and so both need to have the remember picture key applied.

However, even then there are issues with the fact that you are nesting a tikzpicture inside the pgfpicture (which is itself nested in the main tikzpicture) and so just putting remember picture on the outermost tikzpicture does not work. But this is exactly what the \subnode command from the tikzmark library was designed to deal with: it defines a subnode of a node without the rigmarole of setting up a whole new tikzpicture.

So using \subnode and remember picture we get:

\documentclass{article}
%\url{http://tex.stackexchange.com/q/153756/86}
\usepackage{tikz-qtree}
\usetikzlibrary{tikzmark}

\newcommand{\inlinenode}[2]{
There are\\
several line\\
breaks\\
\subnode{#1}{#2} \\
and #1 is not\\
in the center}
\begin{document}
\tikzset{every tree node/.style={align=center,anchor=north}}
\begin{tikzpicture}[remember picture]
\Tree [.{Root}
        [.\node {\inlinenode{x1}{$x_1$}}; ]
        [.\node (x2) {$x_2$}; ]
      ]
\path[thick,color=red] (x1) edge (x2);
\end{tikzpicture}

\end{document}