templating: Add dict unpacking section.

config: Add `parsing` section.

Per iterative/dvc#7907

content/docs/command-reference/config.md

@@ -247,6 +247,77 @@ experiments or projects use a similar structure.
 
 - `exp.live` - path to your [DVCLive](/doc/dvclive) output logs.
 
+### parsing
+
+- `parsing.bool` - Controls the templating syntax for boolean values when used
+  in
+  [dict unpacking](/doc/user-guide/project-structure/pipelines-files#dict-unpacking).
+
+  Valid values are `"store_true"` (default) and `"boolean_optional"`, named
+  after
+  [Python argparse actions](https://docs.python.org/3/library/argparse.html#action).
+
+  Given the following `params.yaml`:
+
+  ```yaml
+  dict:
+    bool-true: true
+    bool-false: false
+  ```
+
+  And corresponding `dvc.yaml`:
+
+  ```yaml
+  stages:
+    foo:
+      cmd: python foo.py ${dict}
+  ```
+
+  When using `store_true`, `cmd` will be:
+
+  ```shell
+  python foo.py --bool-true
+  ```
+
+  Whereas when using `boolean_optional`, `cmd` will be:
+
+  ```shell
+  python foo.py --bool-true --no-bool-false
+  ```
+
+- `parsing.list` - Controls the templating syntax for list values when used in
+  [dict unpacking](/doc/user-guide/project-structure/pipelines-files#dict-unpacking).
+
+  Valid values are `"nargs"` (default) and `"append"`, named after
+  [Python argparse actions](https://docs.python.org/3/library/argparse.html#action).
+
+  Given the following `params.yaml`:
+
+  ```yaml
+  dict:
+    list: [1, 2, 'foo']
+  ```
+
+  And corresponding `dvc.yaml`:
+
+  ```yaml
+  stages:
+    foo:
+      cmd: python foo.py ${dict}
+  ```
+
+  When using `nargs`, `cmd` will be:
+
+  ```shell
+  python foo.py --list 1 2 'foo'
+  ```
+
+  Whereas when using `append`, `cmd` will be:
+
+  ```shell
+  python foo.py --list 1 --list 2 --list 'foo'
+  ```
+
 ### plots
 
 - `plots.html_template` - sets a

content/docs/user-guide/project-structure/pipelines-files.md

@@ -6,17 +6,24 @@ individual [stages](/doc/command-reference/run) in one or more `dvc.yaml` files
 (forming a _dependency graph_, see `dvc dag`). Refer to
 [Get Started: Data Pipelines](/doc/start/data-pipelines).
 
-> Note that a helper command, `dvc stage`, is available to create and list
-> stages.
+<admon type="tip">
+
+A helper command, `dvc stage`, is available to create and list stages.
+
+</admon>
 
 `dvc.yaml` files can be versioned with Git.
 
 These files use the [YAML 1.2](https://yaml.org/) file format, and a
 human-friendly schema explained below. We encourage you to get familiar with it
 so you may modify, write, or generate stages and pipelines on your own.
 
-> Note that we use [GNU/Linux](https://www.gnu.org/software/software.html) in
-> most of our examples.
+<admon type="info">
+
+We use [GNU/Linux](https://www.gnu.org/software/software.html) in most of our
+examples.
+
+</admon>
 
 ## Stages
 
@@ -123,9 +130,6 @@ in the YAML structure itself. These sources can be
 [parameters files](/doc/command-reference/params), or `vars` defined in
 `dvc.yaml` instead.
 
-> Note that this parameterization feature is only supported via manual editing
-> of `dvc.yaml` and incompatible with `dvc run`.
-
 Let's say we have `params.yaml` (default params file) with the following
 contents:
 
@@ -156,6 +160,49 @@ stages:
 DVC will track simple param values (numbers, strings, etc.) used in `${}` (they
 will be listed by `dvc params diff`).
 
+### Dict Unpacking
+
+Only inside the `cmd` entries, you can also reference a dictionary inside `${}`
+and DVC will _unpack_ it. For example, given the following `params.yaml`:
+
+```yaml
+dict:
+  foo: foo
+  bar: 2
+  bool: true
+  nested:
+    foo: bar
+  list: [1, 2, 'foo']
+```
+
+You can reference `dict` in the `cmd` section of a `dvc.yaml`:
+
+```yaml
+stages:
+  train:
+    cmd: python train.py ${dict}
+```
+
+And DVC will _unpack_ the values inside `dict`, creating the following `cmd`
+call:
+
+```shell
+python train.py --foo 'foo' --bar 2 --bool --nested.foo 'bar' --list 1 2 'foo'
+```
+
+This can be useful for avoiding to write every argument passed to the `cmd` or
+having to modify the `dvc.yaml` when adding or removing arguments.
+
+<admon type="tip">
+
+The [parsing](/doc/command-reference/config#parsing) section of `dvc config` can
+be used to customize the syntax used for some ambiguous types like booleans and
+lists.
+
+</admon>
+
+### Vars
+
 Alternatively, values for substitution can be listed as top-level `vars` like
 this:
 
@@ -172,7 +219,11 @@ stages:
     cmd: python train.py --thresh ${models.us.threshold}
 ```
 
-> Note that values from `vars` are not tracked like parameters.
+<admon type="warn">
+
+Values from `vars` are not tracked like parameters.
+
+</admon>
 
 To load additional params files, list them in the top `vars`, in the desired
 order, e.g.: