Nested subgraph labelled same as initial subgraph

I have created nested subgraphs where the top level subgraph should be named “outer subgraph” then the nested subgraph should be named “inner subgraph”:

digraph G {
   subgraph cluster_top_level{
      label="outer subgraph"

      subgraph cluster_inner_level{
         label ="inner subgraph"
}//digraph G

how come the inner subgraph is also labelled “outer subgraph”?

I tried the above input and it showed NO labels (maybe because there are no nodes). Please show a real input file.

I can not have just subgraphs inside of a subgraph with with no nodes and have those nested subgraphs labelled differently from the top level subgraph label? Using all subgraphs is how I got edges to be drawn between a desired node and one of the nested subgraphs which organizes some nodes. Edges either can go from subgraph to subgraph or node to node, from what I have seen. So that is how they all became subgraphs. Ultimately, one subgraph contains an image node, which I would like labelled “UHG assets” and not “Preprocessing” (the label of the outer subgraph):

// Preprocessing cluster
subgraph cluster_preprocessing {
// Formatting for preprocessing cluster
label ="Preprocessing";
fillcolor="#CCFF99"; //light green fill color
node [fillcolor="#F5F5F5" style=filled shape="square"] //node style for cluster_preprocessing

// Subgraphs within cluster_preprocessing
subgraph cluster_uhg_assets{
uhgAssets [fontsize="25", label="UHG assets", //desired label for nested subgraph
labelloc="t",bgcolor="white", size="0.5",

the “UHG assets” label does appear, but the “preprocessing” label also appears right above the image in the Node, which I would like to be “UHG assets” only.

You can have very deeply nested clusters - no problem. But there has to be at least one node somewhere in the nest, and it makes most sense if there is a node in the innermost cluster.
Remember, clusters are created around nodes. If there are no nodes, there is no “place” to put the cluster.
Do you want “UHG assets” to be a node label or a cluster label? It is currently defined as a node label, but the comment seems to say it should be a cluster label.