Docs: Clarify --ext only works with directories (fixes #7939) (#8095)

docs/developer-guide/nodejs-api.md

@@ -164,7 +164,7 @@ The `CLIEngine` is a constructor, and you can create a new instance by passing i
 * `configFile` - The configuration file to use (default: null). Corresponds to `-c`.
 * `cwd` - Path to a directory that should be considered as the current working directory.
 * `envs` - An array of environments to load (default: empty array). Corresponds to `--env`.
-* `extensions` - An array of filename extensions that should be checked for code. The default is an array containing just `".js"`. Corresponds to `--ext`.
+* `extensions` - An array of filename extensions that should be checked for code. The default is an array containing just `".js"`. Corresponds to `--ext`. It is only used in conjunction with directories, not with filenames or glob patterns.
 * `fix` - True indicates that fixes should be included with the output report, and that errors and warnings should not be listed if they can be fixed. However, the files on disk will not be changed. To persist changes to disk, call [`outputFixes()`](#outputfixes).
 * `globals` - An array of global variables to declare (default: empty array). Corresponds to `--global`.
 * `ignore` - False disables use of `.eslintignore`, `ignorePath` and `ignorePattern` (default: true). Corresponds to `--no-ignore`.

docs/user-guide/command-line-interface.md

@@ -80,9 +80,9 @@ Options that accept array values can be specified by repeating the option or wit
 
 Example:
 
-    eslint --ext .jsx --ext .js file.js
+    eslint --ext .jsx --ext .js lib/
 
-    eslint --ext .jsx,.js file.js
+    eslint --ext .jsx,.js lib/
 
 ### Basic configuration
 
@@ -137,7 +137,8 @@ Examples:
     # Also use both .js and .js2
     eslint . --ext .js,.js2
 
-**Note:** If you use a glob pattern, then `--ext` is ignored
+**Note:** `--ext` is only used when the arguments are directories. If you use glob patterns or file names, then `--ext` is ignored.
+
 For example, `eslint lib/* --ext .js` will match all files within the `lib/` directory, regardless of extension.
 
 #### `--global`

docs/user-guide/configuring.md

@@ -728,7 +728,7 @@ Both the JSON and YAML configuration file formats support comments (`package.jso
 
 ## Specifying File extensions to Lint
 
-Currently the sole method for telling ESLint which file extensions to lint is by specifying a comma separated list of extensions using the [`--ext`](./command-line-interface#ext) command line option.
+Currently the sole method for telling ESLint which file extensions to lint is by specifying a comma separated list of extensions using the [`--ext`](./command-line-interface#ext) command line option. Note this flag only takes effect in conjunction with directories, and will be ignored if used with filenames or glob patterns.
 
 ## Ignoring Files and Directories