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/inject-data-application/define-environment-variable-container.md

@@ -32,6 +32,11 @@ 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,
+If the `RelaxedEnvironmentVariableValidation` [feature gate](/docs/reference/command-line-tools-reference/feature-gates/) is enabled, all [printable ASCII characters](https://www.ascii-code.com/characters/printable-characters) except "=" may be used for environment variable 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).