TikZ - tikzpicture nested in \graph node

Question

I am trying to nest tikz graph environments into the nodes of a tikz graph environment:

\begin{tikzpicture}
    \graph [layered layout]{
        ABABAB -> {
            AB -> {A, B},
            BA -> {A, B}
        };
    };
\end{tikzpicture}

I got this so far and I need to make each node its own graph with a similar layout.

I also want to be able to connect nodes from the inner graphs with nodes of the outer graph.

I could create all nodes individually and connect them, with nested nodes like this:

\node [draw] at (0,0) (container1) {
    \begin{tikzpicture}
        \node at (0,0) (container1label) {Node 1};
        \node [draw,below=0.4 of container1label] (child1) {Node 1's Child};
    \end{tikzpicture}
};

But I would like to have the layout automatically taken care of.

Ideally I would create the outer graph with invisible edges, so the layout is appropriate, and then connect the inner nodes of the graphs with each other manually.

Is there some way to nest a tikzpicture in a node created in a \graph environment?

Edit:

To make it more clear, this is what I am trying to model. A formal grammar composed of rules. I need an outer node for each left side of a rule and inside these outer nodes I would like to be able to create new nodes for each symbol and connect them with their corresponding outer nodes.

For example, I would like the outer node of abcdef to contain nodes for ab, cde, f, a, bc and def (preferrably easily laid out as shown in the picture, in two lines) and then I need an edge from each of these inner nodes to their corresponding outer node, which in turn contains its rule's symbols.

A simpler solution might be to only connect the outer nodes with each other if they have rules pointing to each other, but I wouldn't even know how to define a math text content for each node in the graph environment. Preferrably I would like to connect each inner symbol node with each outer rule node, though.

So similar to this:

Answer 1

The sublayouts certainly provide one solution for this.

Code

% !TeX TS-program = lualatex
\documentclass[tikz]{standalone}
\usetikzlibrary{graphs, graphdrawing}
\usegdlibrary{layered}
\begin{document}
\tikz[
  text depth=+0pt, text height=+.7em, inner sep=+.2em,
  subgraph text none, anchor=base,
  subgraph nodes={
    draw=lightgray, rectangle, rounded corners, inner sep=+.333em,
    text depth=, text height=}]
\graph [layered layout, fresh nodes, nodes behind edges] {
  XYABCDEFXY//[layered layout]{ xyabcdefxy -- { xy, abcdef, xy } },
  XY//[layered layout]{ xy -- {x, y} },
  ABCDEF//[layered layout]{
    abcdef -- {
      ab  -- { a,    bc  },
      cde -- { (bc), def }, % (bc) to connect to the previous bc node
      f   -- (def)          % and not create a new one
    }
  },
  AB //[layered layout]{ ab  -- { a,  b  }},
  CDE//[layered layout]{ cde -- { c,  de }},
  BC //[layered layout]{ bc  -- { b,  c  }},
  DEF//[layered layout]{ def -- { de, f  }},
  DE //[layered layout]{ de  -- { d,  e  }},
  % all nodes in () because we want to use the existing ones
  {(xy), (xy')} -- (XY),
  (abcdef) --               (ABCDEF),
  (ab)     --               (AB),
  (cde)    --[bend left=15] (CDE),
  (bc)     --               (BC),
  (def)    --               (DEF),
  (de)     --               (DE)
};
\end{document}

Output