[doc] RUM Privacy Plugin

packages/plugins/rum/src/privacy/README.md

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+# RUM Privacy Plugin <!-- #omit in toc -->
+
+The RUM Privacy Plugin provides action name and session replay masking capabilities for Real User Monitoring (RUM). This plugin helps protect sensitive data while maintaining observability. See [Action Name Deobfuscation](https://docs.datadoghq.com/real_user_monitoring/application_monitoring/browser/build_plugins/action_name_deobfuscation/).
+
+## Use Cases
+
+This plugin is particularly useful for:
+
+- Masking sensitive data **before** sending them to Datadog
+- Providing an out-of-the-box solution with minimal instrumentation overhead
+- Maintaining observability while ensuring privacy compliance
+
+## Reserved Global Variables
+
+The following global variable is used by this plugin:
+
+- `$DD_ALLOW` - Contains raw static strings from source code
+- `$DD_A_Q` - Manage the queue of adding to allowlist at runtime
+
+## File Inclusion/Exclusion for String Literal Extraction
+
+### Default Settings
+
+Excludes:
+
+- `node_modules` directories
+- `.preval` files
+- Files that start with special characters
+Includes:
+- files matching `/\.(?:c|m)?(?:j|t)sx?$/`
+
+To instantiate the plugin with default settings:
+
+```javascript
+const { datadogWebpackPlugin } = require('@datadog/webpack-plugin');
+
+module.exports = {
+  plugins: [
+    datadogWebpackPlugin({
+      rum: {
+        privacy: {},
+      },
+    }),
+  ],
+};
+```
+
+### Overrides
+
+You can override file inclusion/exclusion using regular expressions:
+
+```javascript
+module.exports = {
+  plugins: [
+    datadogWebpackPlugin({
+      rum: {
+        privacy: {
+          include: [/packages\/apps\/.*\.(?:c|m)?(?:j|t)sx?$/],
+          exclude: [/\/node_modules\//, /\/test\//],
+        },
+      },
+    }),
+  ],
+};
+```
+
+> Note: if you are overriding the default setting, please make sure that you are aligned with the default setting.
+
+### Excluding Code Blocks with Comments
+
+#### Single Line
+
+```javascript
+  "exclude line 1", // datadog-privacy-allowlist-exclude-line
+  "exclude line 2", /* datadog-privacy-allowlist-exclude-line */
+
+  /* datadog-privacy-allowlist-exclude-line */ "exclude line 3",
+
+  /*
+   datadog-privacy-allowlist-exclude-line
+   */ "exclude line 4",
+```
+
+#### Next Line
+
+```javascript
+  // datadog-privacy-allowlist-exclude-next-line
+  "exclude next line 1",
+
+  /* datadog-privacy-allowlist-exclude-next-line */
+  "exclude next line 2",
+
+  /*
+   datadog-privacy-allowlist-exclude-next-line
+   */
+  `exclude next line 3`,
+```
+
+#### Multi-line/Blocks
+
+```javascript
+  // datadog-privacy-allowlist-exclude-begin
+  "exclude range 1",
+  'exclude range 2',
+  `exclude range 3`,
+  // datadog-privacy-allowlist-exclude-end
+
+  /* datadog-privacy-allowlist-exclude-begin */
+  "exclude range with block comment 1",
+  'exclude range with block comment 2',
+  `exclude range with block comment 3`,
+  /* datadog-privacy-allowlist-exclude-end */
+
+
+  // An unterminated 'exclude-begin' should cover the rest of the file. (And extra
+  // 'exclude-begins' after that point should be ignored.)
+  /* datadog-privacy-allowlist-exclude-begin */
+  "exclude range with unterminated comment 1",
+  'exclude range with unterminated comment 2',
+  /* datadog-privacy-allowlist-exclude-begin */
+  `exclude range with unterminated comment 3`,
+```