Add documentation for the "keys" node.

Author: fdb

node/reference/index.md

@@ -129,6 +129,7 @@ List
 * [Cull](/node/reference/list/cull.html): Remove all items from the list where the corresponding boolean is false.
 * [Distinct](/node/reference/list/distinct.html): Remove all duplicate items from the list.
 * [First](/node/reference/list/first.html): Take the first item of the list.
+* [Keys](/node/reference/list/keys.html): Retrieve the keys of a map.
 * [Last](/node/reference/list/last.html): Take the last item of the list.
 * [Pick](/node/reference/list/pick.html): Pick items from the list in random order.
 * [Repeat](/node/reference/list/repeat.html): Repeat the list a number of times.

node/reference/list/index.md

@@ -9,6 +9,7 @@ notes: AUTO-GENERATED - DO NOT EDIT. Use the autoref.py script to re-generate th
 * [Cull](/node/reference/list/cull.html): Remove all items from the list where the corresponding boolean is false.
 * [Distinct](/node/reference/list/distinct.html): Remove all duplicate items from the list.
 * [First](/node/reference/list/first.html): Take the first item of the list.
+* [Keys](/node/reference/list/keys.html): Retrieve the keys of a map.
 * [Last](/node/reference/list/last.html): Take the last item of the list.
 * [Pick](/node/reference/list/pick.html): Pick items from the list in random order.
 * [Repeat](/node/reference/list/repeat.html): Repeat the list a number of times.

node/reference/list/keys.md

@@ -0,0 +1,15 @@
+---
+layout: reference
+library: list
+node: keys
+title: Keys
+image: keys.png
+---
+Retrieve the keys of a map.
+
+* **Map**: The input map.
+
+## Notes
+* This node can be used to retrieve the headers of a [CSV file](/node/reference/data/import_csv.html).
+* This node also lists the properties of graphic objects, like a [rect](/node/reference/corevector/rect.html) node. You can use this list with the [lookup](/node/reference/data/lookup.html) node, for example to retrieve the `bounds`.
+