Allow almost all printable ASCII characters in environment variables

Author: HirazawaUi

content/en/docs/reference/command-line-tools-reference/feature-gates/relaxed-environment-variable-validation.md

@@ -0,0 +1,13 @@
+---
+title: RelaxedEnvironmentVariableValidation
+content_type: feature_gate
+_build:
+  list: never
+  render: false
+
+stages:
+  - stage: alpha
+    defaultValue: false
+    fromVersion: "1.30"
+---
+Allow almost all printable ASCII characters in environment variables.

content/en/docs/tasks/configure-pod-container/configure-pod-configmap.md

@@ -557,6 +557,12 @@ section, and learn how to use these objects with Pods.
 
    Now, the Pod's output includes environment variable `SPECIAL_LEVEL_KEY=very`.
 
+{{< note >}}
+The range of characters allowed by env names is smaller than the range of characters allowed by configmap keys, it does not allow it to start with a number.
+after enable the `RelaxedEnvironmentVariableValidation` [feature gate](/docs/reference/command-line-tools-reference/feature-gates/), the name of env allows a wider range of characters,
+then all configmap keys can be set to env names
+{{< /note >}}
+
 ### Define container environment variables with data from multiple ConfigMaps
 
 As with the previous example, create the ConfigMaps first.

content/en/docs/tasks/inject-data-application/define-environment-variable-container.md

@@ -32,6 +32,12 @@ The `env` and `envFrom` fields have different effects.
  are set as environment variables for the container.
  You can also specify a common prefix string.
 
+{{< note >}}
+The allowed character range of env name is within C_IDENTIFIER,
+after enable the `RelaxedEnvironmentVariableValidation` [feature gate](/docs/reference/command-line-tools-reference/feature-gates/), the name of env allows a wider range of characters,
+all printable ASCII characters except "=" can be used in env names.
+{{< /note >}}
+
 You can read more about [ConfigMap](/docs/tasks/configure-pod-container/configure-pod-configmap/#configure-all-key-value-pairs-in-a-configmap-as-container-environment-variables)
 and [Secret](/docs/tasks/inject-data-application/distribute-credentials-secure/#configure-all-key-value-pairs-in-a-secret-as-container-environment-variables).
 
@@ -41,7 +47,6 @@ In this exercise, you create a Pod that runs one container. The configuration
 file for the Pod defines an environment variable with name `DEMO_GREETING` and
 value `"Hello from the environment"`. Here is the configuration manifest for the
 Pod:
-
 {{% code_sample file="pods/inject/envars.yaml" %}}
 
 1. Create a Pod based on that manifest: