Name a port apart from its message in the node panel, two lines per port

The port name follows the message until it is typed by hand, and clearing
it follows again. The second line holds the message, so a list port's item
type no longer squeezes the name.

docs/interface/flow-editor.md

@@ -35,11 +35,20 @@ the canvas with its panel open.
 
 Floats on the right; a full-screen sheet on a phone.
 
-**Consumes** and **Provides** are the ports. Each row is a message name, a
-payload type, and, on an output, a *streaming* toggle for ports that publish
-repeatedly during one execution. The name field suggests messages already in
-the flow, which is usually how you wire something: type the name that already
-exists.
+**Consumes** and **Provides** are the ports. Each port has two lines: its name
+and payload type (a `list` also says what its items are), then the message it
+is bound to, how often at most it is delivered, and, on an output, a
+*streaming* toggle for ports that publish repeatedly during one execution. The
+message field suggests messages already in the flow, which is usually how you
+wire something: type the name that already exists.
+
+A port is named after its message until you name it yourself. Its name field
+then stays empty and shows the name it follows. A name typed there stays when
+the message changes, which is how a port is bound to a message called
+something else, as a [`wren`](../reference/node-types.md#wren) target is;
+clear it to follow the message again. The name is what the node's code sees,
+so it is letters, digits and `_`, not starting with a digit, and no two inputs
+or two outputs of a node share one. The field keeps the name it had otherwise.
 
 Renaming an output renames the message everywhere it is read. Inputs are not
 renamed, because an input is more often re-pointed at a different message than

docs/reference/node-types.md

@@ -321,10 +321,10 @@ that is not wired to the node.
   `heat`, `boost` for heating; `media`, `music`, `tv`; `shutter`, `blind`,
   `cover`; `water`, `watering`, `sprinkler`
 
-A port naming anything else is refused when the flow is built. The editor
-names a port after its message, so there a target's message carries the name;
-binding a port to a message named otherwise, as `{"name": "setpoint", "port":
-"living_room_setpoint"}`, takes the flow API.
+A port naming anything else is refused when the flow is built. A port is
+named after its message unless it is given a name of its own, in the node
+panel's port name field or as `{"name": "setpoint", "port":
+"living_room_setpoint"}` through the flow API.
 
 Targets of one area and kind are one device to the model, and each takes what
 a call means for its type. A target's current value is the state the model