Doc fix: explain the details of setting Graphviz/D2 output defaults

docs/netlab/create.md

@@ -88,13 +88,14 @@ Without specifying the output format(s), **netlab create** creates a provider co
 
 You could specify one or more output formats with the `-o` CLI parameter. For more details please read the [output formats](../outputs/index.md) part of the documentation.
 
+(netlab-create-set)=
 ## Setting Topology Parameters from Command Line
 
 The following CLI flags can be used to change individual topology parameters:
 
 * `-d` sets default device type (**defaults.device**)
 * `-p` sets virtualization provider (**provider**)
-* `-s` uses `key=value` format to set specified topology element  value. The key could be a hierarchical dotted name.
+* `-s` uses the `key=value` format to set the specified topology element's value. The key could be a hierarchical dotted name.
 * `--plugin` specifies additional plugins not listed in lab topology or system defaults (example: multilab plugin)
 
 ### Example

docs/netlab/graph.md

@@ -1,3 +1,4 @@
+(netlab-graph)=
 # Creating Physical or BGP Topology Graphs
 
 **netlab graph** command creates a graph description in [Graphviz](https://graphviz.org/) or [D2](https://d2lang.com/) format from the transformed lab topology data (usually stored in `netlab.snapshot.yml`) created by **netlab create** command. It's replicating the functionality of **netlab create -o graph:_name_** command with a more convenient user interface. 

docs/outputs/d2.md

@@ -15,16 +15,16 @@ The network topology graph description contains nodes and links but no placement
 
 ## Modifying Graph Attributes
 
-Graphing routines use **default** topology settings to modify the node- or link parameters of the generated D2 file:
+Graphing routines use **[default](defaults)** topology settings to modify the node- or link parameters of the generated D2 file:
 
 * **outputs.d2.interface_labels** (default: False) -- Add IP addresses to links in **topology** graph. Results in a cluttered image.
 * **outputs.d2.groups** (default: None) -- use the specified list of groups (or all groups when set to *True*) to create graph clusters
 * **outputs.d2.node_address_label** (default: True) -- add node loopback IP addresses or IP addresses of the first interface (for hosts) to node labels.
 * **outputs.d2.node_interfaces** (default: False) -- add list of interfaces and their IP addresses to nodes[^DG].
-* **outputs.d2.as_clusters** (default: True) -- use BGP autonomous systems to cluster nodes in topology graph. BGP AS clusters are always used in BGP graphs.
+* **outputs.d2.as_clusters** (default: True) -- use BGP autonomous systems to cluster nodes in the topology graph. BGP AS clusters are always used in BGP graphs.
 * **outputs.d2.rr_sessions** (default: True) -- draw IBGP sessions between BGP route reflectors and clients as directional connections.
 
-[^DG]: The results look disgusting. If you find a better way to get it done please submit a PR. Thank you!
+[^DG]: The results look disgusting. If you find a better way to get it done, please submit a PR. Thank you!
 
 ## Modifying Shape and Connection Attributes
 
@@ -66,12 +66,16 @@ ebgp:
 
 ## Specifying D2 Attributes
 
-You could specify D2 attributes in your topology file, in per-user topology defaults, or in system defaults ([more details](../defaults.md)). You could also specify them with `-s` parameter of **netlab create** command ([more details](../netlab/create.md)).
+You could specify D2 attributes in your [topology file](defaults-topology) (where you would have to prefix them with **defaults**), in [per-user topology defaults](defaults-user-file), or with [environment variables](defaults-env) (even [more details](../defaults.md)). You could also specify them with the `-s` parameter of the **[netlab create](netlab-create)** command, yet again prefixed with **defaults** ([more details](netlab-create-set)).
 
-Use the `netlab create -o yaml:defaults.outputs.d2` to show the actual D2 defaults including topology file defaults and user defaults, for example:
+Use the **netlab show defaults outputs.d2** [command](netlab-show-defaults) to show the current D2 defaults, including topology file defaults and user defaults, for example:
 
 ```
-$ netlab create -o yaml:defaults.outputs.d2
+% netlab show defaults outputs.d2
+
+netlab default settings within the outputs.d2 subtree
+=====================================================
+
 as_clusters: true
 ebgp:
   source-arrowhead:
@@ -94,10 +98,15 @@ lan:
   shape: rectangle
   style:
     border-radius: 8
+    font-size: 20
 node_address_label: true
 router:
   shape: oval
+  style:
+    font-size: 20
 rr_sessions: true
 switch:
   shape: hexagon
+  style:
+    font-size: 20
 ```

docs/outputs/graph.md

@@ -4,24 +4,26 @@
 
 **Note**: The network topology graph description contains nodes and links but no placement information. *graphviz* is pretty good at figuring out how to draw the required graph, but it pays out to test out various [layout engines](https://graphviz.org/docs/layouts/) (hint: use the name of the layout engine as the [CLI command](https://graphviz.org/doc/info/command.html)).
 
-The *graph* output module is invoked by specifying `-o graph` parameter in **netlab create** command. It takes an optional destination file name (default: `graph.dot`).
+The *graph* output module is invoked with the **[netlab graph](netlab-graph)** command or by specifying the `-o graph` parameter in the **netlab create** command. It takes an optional destination file name (default: `graph.dot`).
 
 A single formatting modifier can be used to specify the graph type:
 
-* **topology** (default) -- Include, physical links, and multi-access- and stub subnets. When the network topology contains BGP information, the graph groups nodes into autonomous systems. Alternatively, you could set **defaults.outputs.graph.groups** attribute to use topology **[groups](../groups.md)** to group graph nodes.
+* **topology** (default) -- Display inter-node links, multi-access- and stub subnets. When the network topology contains BGP information, the graph groups nodes into autonomous systems. Alternatively, you could set **defaults.outputs.graph.groups** attribute to use topology **[groups](../groups.md)** to group graph nodes.
 * **bgp** -- Include autonomous systems, nodes, and BGP sessions. With the **rr** option (specified with `netlab create -o graph:bgp:rr`), RR-client sessions are drawn as directed arrows.
 
 ## Modifying Graph Attributes
 
-Graphing routines use **default** topology settings to modify the node- or link parameters of the generated DOT file:
+Graphing routines use **[default](defaults)** topology settings to modify the generated DOT file's node- or link parameters. You can change these defaults.
 
 * **outputs.graph.interface_labels** -- Add IP addresses to links in **topology** graph. Results in a cluttered image (but feel free to fix that and submit a pull request).
 * **outputs.graph.colors._object_** -- Specify background color for *as*, *node*, *stub* subnet, *ibgp* or *ebgp* session.
 * **outputs.graph.margins.as** -- Inner margin for graph clusters (BGP autonomous system or groups).
 * **outputs.graph.groups** -- use the specified list of groups (or all groups when set to *True*) to create graph clusters
 * **outputs.graphs.node_address_labels** -- add node loopback IP addresses or IP addresses of the first interface (for hosts) to node labels.
 
-You could specify these attributes in your topology file, in per-user topology defaults, or in system defaults ([more details](../defaults.md)). You could also specify them with `-s` parameter of **netlab create** command ([more details](../netlab/create.md)). The system defaults in *netlab* release 1.2.4 are included below:
+You could specify these attributes in your [topology file](defaults-topology) (where you would have to prefix them with **defaults**), in [per-user topology defaults](defaults-user-file), or with [environment variables](defaults-env) (even [more details](../defaults.md)). You could also specify them with the `-s` parameter of the **[netlab create](netlab-create)** command, yet again prefixed with **defaults** ([more details](netlab-create-set)).
+
+The system defaults in *netlab* release 1.9.1 are included below; you can always inspect them with **netlab show defaults outputs.graph**
 
 ```
 outputs: