Add a stub page on function packages

Signed-off-by: Nic Cope <[email protected]>

Author: negz

content/v2.0-preview/packages/configurations.md

@@ -10,19 +10,18 @@ A _Configuration_ package is an
 [Compositions]({{<ref "../composition/compositions" >}}), 
 [Composite Resource Definitions]({{<ref "../composition/composite-resource-definitions" >}})
 and any required [Providers]({{<ref "./providers">}}) or 
-[Functions]({{<ref "../composition/compositions" >}}).
+[Functions]({{<ref "./functions" >}}).
 
 Configuration packages make your Crossplane configuration fully portable. 
 
 {{<hint "important" >}}
-Crossplane [Providers]({{<ref "./providers">}}) and 
-[Functions]({{<ref "../composition/compositions">}}) are also Crossplane packages.  
+Crossplane Providers and Functions are also Crossplane packages.  
 
 This document describes how to install and manage configuration packages.  
 
 Refer to the 
 [Provider]({{<ref "./providers">}}) and 
-[Composition Functions]({{<ref "../composition/compositions">}}) chapters for
+[Functions]({{<ref "./functions">}}) chapters for
 details on their usage of packages. 
 {{< /hint >}}
 

content/v2.0-preview/packages/functions.md

@@ -0,0 +1,79 @@
+---
+title: Functions
+weight: 100
+description: "Functions extend Crossplane with new ways to configure composition"
+---
+
+Functions extend Crossplane with new ways to configure
+[composition]({{<ref "../composition">}}).
+
+You can use different _composition functions_ to configure what Crossplane does
+when someone creates or updates a
+[composite resource (XR)]({{<ref "../composition/composite-resources">}}).
+
+{{<hint "important">}}
+This page is a work in progress.
+
+Functions are packages, like [Providers]({{<ref "./providers">}}) and
+[Configurations]({{<ref "./configurations">}}). Their APIs are similar. You
+install and configure them the same way as a provider.
+
+Read the [composition]({{<ref "../composition/compositions">}}) documentation to
+learn how to use functions in a composition.
+{{</hint>}}
+
+## Install a Function
+
+Install a Function with a Crossplane
+{{<hover label="install" line="2">}}Function{{</hover >}} object setting the
+{{<hover label="install" line="6">}}spec.package{{</hover >}} value to the
+location of the function package.
+
+{{< hint "important" >}}
+Beginning with Crossplane version 1.20.0 Crossplane uses the [crossplane-contrib](https://github.com/orgs/crossplane-contrib/packages) GitHub Container Registry at `xpkg.crossplane.io` by default for downloading and
+installing packages. 
+
+Specify the full domain name with the `package` or change the default Crossplane
+registry with the `--registry` flag on the [Crossplane pod]({{<ref "../guides/pods">}})
+{{< /hint >}}
+
+For example, to install the
+[patch and transform function](https://github.com/crossplane-contrib/function-patch-and-transform),
+
+```yaml {label="install"}
+apiVersion: pkg.crossplane.io/v1
+kind: Function
+metadata:
+  name: crossplane-contrib-function-patch-and-transform
+spec:
+  package: xpkg.crossplane.io/crossplane-contrib/function-patch-and-transform:v0.8.2
+```
+
+By default, the Function pod installs in the same namespace as Crossplane
+(`crossplane-system`).
+
+{{<hint "note" >}}
+Functions are part of the 
+{{<hover label="install" line="1">}}pkg.crossplane.io{{</hover>}} group.  
+
+The {{<hover label="meta-pkg" line="1">}}meta.pkg.crossplane.io{{</hover>}}
+group is for creating Function packages. 
+
+Instructions on building Functions are outside of the scope of this
+document.  
+Read the Crossplane contributing 
+[Function Development Guide](https://github.com/crossplane/crossplane/blob/main/contributing/guide-provider-development.md)
+for more information.
+
+For information on the specification of Function packages read the 
+[Crossplane Function Package specification](https://github.com/crossplane/crossplane/blob/main/contributing/specifications/xpkg.md#provider-package-requirements).
+
+```yaml {label="meta-pkg"}
+apiVersion: meta.pkg.crossplane.io/v1
+kind: Function
+metadata:
+  name: provider-aws
+spec:
+# Removed for brevity
+```
+{{</hint >}}