docs: YAML: Add `arg_flattening: false` where required
diff --git a/docs/yaml/builtins/meson.yaml b/docs/yaml/builtins/meson.yaml
index 09e5dbb..1ae3499 100644
--- a/docs/yaml/builtins/meson.yaml
+++ b/docs/yaml/builtins/meson.yaml
@@ -259,6 +259,7 @@
 
       This method is replaced by [[meson.get_external_property]].
 
+    arg_flattening: false
     posargs_inherit: meson.get_external_property
     optargs_inherit: meson.get_external_property
 
@@ -269,6 +270,8 @@
       Returns the given property from a native or cross file.
       The optional fallback_value is returned if the given property is not found.
 
+    arg_flattening: false
+
     posargs:
       propname:
         type: str
diff --git a/docs/yaml/elementary/dict.yml b/docs/yaml/elementary/dict.yml
index 5afe835..f3ca837 100644
--- a/docs/yaml/elementary/dict.yml
+++ b/docs/yaml/elementary/dict.yml
@@ -30,6 +30,8 @@
     fallback value given as the second argument. If a single argument
     was given and the key was not found, causes a fatal error
 
+  arg_flattening: false
+
   posargs:
     key:
       type: str
diff --git a/docs/yaml/elementary/list.yml b/docs/yaml/elementary/list.yml
index 085b6ca..1ffb6d2 100644
--- a/docs/yaml/elementary/list.yml
+++ b/docs/yaml/elementary/list.yml
@@ -10,6 +10,8 @@
     Returns `true` if the array contains the object
     given as argument, `false` otherwise
 
+  arg_flattening: false
+
   posargs:
     item:
       type: any
@@ -23,6 +25,8 @@
     bounds returns the `fallback` value *(since 0.38.0)* or, if it is
     not specified, causes a fatal error
 
+  arg_flattening: false
+
   posargs:
     index:
       type: int
diff --git a/docs/yaml/elementary/str.yml b/docs/yaml/elementary/str.yml
index b79577a..9c4ec9d 100644
--- a/docs/yaml/elementary/str.yml
+++ b/docs/yaml/elementary/str.yml
@@ -21,6 +21,8 @@
     # res now has value 'string: text, number: 1, bool: true'
     ```
 
+  arg_flattening: false
+
   posargs:
     fmt:
       description: |
diff --git a/docs/yaml/functions/environment.yaml b/docs/yaml/functions/environment.yaml
index 5fb81e3..5c3a43d 100644
--- a/docs/yaml/functions/environment.yaml
+++ b/docs/yaml/functions/environment.yaml
@@ -3,6 +3,8 @@
 since: 0.35.0
 description: Returns an empty [[@env]] object.
 
+arg_flattening: false
+
 optargs:
   env:
     type: str | list[str] | dict[str] | dict[list[str]]
diff --git a/docs/yaml/functions/error.yaml b/docs/yaml/functions/error.yaml
index f4bb84c..628e5b8 100644
--- a/docs/yaml/functions/error.yaml
+++ b/docs/yaml/functions/error.yaml
@@ -2,6 +2,8 @@
 returns: void
 description: Print the argument string and halts the build process.
 
+arg_flattening: false
+
 posargs:
   message:
     type: str
diff --git a/docs/yaml/functions/get_variable.yaml b/docs/yaml/functions/get_variable.yaml
index f8177c1..78bd7fd 100644
--- a/docs/yaml/functions/get_variable.yaml
+++ b/docs/yaml/functions/get_variable.yaml
@@ -8,6 +8,8 @@
   `res`instead. If a fallback is not specified, then attempting to read
   a non-existing variable will cause a fatal error.
 
+arg_flattening: false
+
 posargs:
   variable_name:
     type: str
diff --git a/docs/yaml/functions/message.yaml b/docs/yaml/functions/message.yaml
index 9d832c1..e480457 100644
--- a/docs/yaml/functions/message.yaml
+++ b/docs/yaml/functions/message.yaml
@@ -2,6 +2,8 @@
 returns: void
 description: This function prints its argument to stdout.
 
+arg_flattening: false
+
 posargs:
   text:
     type: str | int | bool | list[str | int | bool] | dict[str | int | bool]
diff --git a/docs/yaml/functions/set_variable.yaml b/docs/yaml/functions/set_variable.yaml
index 19dc2e1..e9b5db3 100644
--- a/docs/yaml/functions/set_variable.yaml
+++ b/docs/yaml/functions/set_variable.yaml
@@ -6,6 +6,8 @@
 
   *(since 0.46.1)* The `value` parameter can be an array type.
 
+arg_flattening: false
+
 posargs:
   variable_name:
     type: str
diff --git a/docs/yaml/functions/summary.yaml b/docs/yaml/functions/summary.yaml
index 29bff0b..cf63dcd 100644
--- a/docs/yaml/functions/summary.yaml
+++ b/docs/yaml/functions/summary.yaml
@@ -61,6 +61,8 @@
                        True
   ```
 
+arg_flattening: false
+
 posargs:
   key_or_dict:
     type: str | dict[str | bool | int | dep | external_program | list[str | bool | int | dep | external_program]]
diff --git a/docs/yaml/functions/warning.yaml b/docs/yaml/functions/warning.yaml
index f4bb0ec..64b1a03 100644
--- a/docs/yaml/functions/warning.yaml
+++ b/docs/yaml/functions/warning.yaml
@@ -3,5 +3,7 @@
 since: 0.44.0
 description: This function prints its argument to stdout prefixed with WARNING:.
 
+arg_flattening: false
+
 posargs_inherit: message
 varargs_inherit: message
diff --git a/docs/yaml/objects/subproject.yaml b/docs/yaml/objects/subproject.yaml
index d84e3f0..1fe8c37 100644
--- a/docs/yaml/objects/subproject.yaml
+++ b/docs/yaml/objects/subproject.yaml
@@ -19,6 +19,8 @@
     If a fallback is not specified, then attempting to read a non-existing
     variable will cause a fatal error.
 
+  arg_flattening: false
+
   posargs:
     var_name:
       type: str