## `attribute_changed` event hook

In a cookbook library file, you can add this in order to print out all attribute changes in cookbooks:

```ruby
Chef.event_handler do
  on :attribute_changed do |precedence, key, value|
    puts "setting attribute #{precedence}#{key.map {|n| "[\"#{n}\"]" }.join} = #{value}"
  end
end
```

If you want to setup a policy that override attributes should never be
used:

```ruby
Chef.event_handler do
  on :attribute_changed do |precedence, key, value|
    raise "override policy violation" if precedence == :override
  end
end
```

## Automatic connection to Chef Automate's data collector with supported Chef server

Chef client will automatically attempt to connect to the Chef server
authenticated data collector proxy. If you have a supported version of
Chef server with this feature enabled, Chef client run data will
automatically be forwarded to Chef Automate without additional Chef
client configuration. If you do not have Chef Automate, or the feature
is disabled on the Chef server, Chef client will detect this and disable
data collection.

<div class="admonition-note">
<p class="admonition-note-title">Note</p>
<div class="admonition-note-text">

Chef Infra Server 12.11.0 or newer is required for this feature.

</div>
</div>

## RFC018 Partially Implemented: Specify `--field-separator` for attribute filtering

If you have periods (`.`) in your Chef Node attribute keys, you can now pass the `--field-separator` (or `-S`) flag along with your `--attribute` (or `-a`) flag to specify a custom nesting character other than `.`.

In a situation where the *webapp* node has the following node data:

```javascript
{
  "foo.bar": "baz",
  "alpha": {
    "beta": "omega"
  }
}
```

Running `knife node show` with the default field separator (`.`) won't show us the data we're expecting for the `foo.bar` attribute because of the period:

```bash
knife node show webapp -a foo.bar
webapp:
  foo.bar:

knife node show webapp -a alpha.beta
webapp:
  alpha.beta: omega
```

However, by specifying a field separator other than `.` we are now able to show the data.

```bash
knife node show webapp -S: -a foo.bar
webapp:
  foo.bar: baz

knife node show webapp -S: -a alpha:beta
webapp:
  alpha:beta: omega
```

## Package locking for Apt, Yum, and Zypper

To allow for more fine grain control of package installation the
`apt_package`, `yum_package`, and `zypper_package` resources now support
the `:lock` and `:unlock` actions.

```ruby
package "httpd" do
  action :lock
end

package "httpd" do
  action :unlock
end
```