Use boolean selector syntax for tags.

README.md

 `test` provides a standard way of writing and running tests in Dart.
 
 * [Writing Tests](#writing-tests)
 * [Running Tests](#running-tests)
   * [Restricting Tests to Certain Platforms](#restricting-tests-to-certain-platforms)
   * [Platform Selectors](#platform-selectors)
   * [Running Tests on Dartium](#running-tests-on-dartium)
 * [Asynchronous Tests](#asynchronous-tests)
 * [Running Tests With Custom HTML](#running-tests-with-custom-html)
 * [Configuring Tests](#configuring-tests)
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 [package configuration file][configuring tags], it'll print a warning, so be
 sure to include all your tags there. You can also use the file to provide
 default configuration for tags, like giving all `browser` tests twice as much
 time before they time out.
 
 [configuring tags]: https://github.com/dart-lang/test/blob/master/doc/package_config.md#configuring-tags
 
 Tests can be filtered based on their tags by passing command line flags. The
 `--tags` or `-t` flag will cause the test runner to only run tests with the
 given tags, and the `--exclude-tags` or `-x` flag will cause it to only run
-tests *without* the given tags.
+tests *without* the given tags. These flags also support
+[boolean selector syntax][]. For example, you can pass `--tags "(chrome ||
+firefox) && !slow"` to select quick Chrome or Firefox tests.
 
 Note that tags must be valid Dart identifiers, although they may also contain
 hyphens.
 
 ### Whole-Package Configuration
 
 For configuration that applies across multiple files, or even the entire
 package, `test` supports a configuration file called `dart_test.yaml`. At its
 simplest, this file can contain the same sort of configuration that can be
 passed as command-line arguments:
@@ skipping 95 matching lines @@
 available to tests.
 
 [api]: http://www.dartdocs.org/documentation/test/latest/index.html
 
 The test runner also supports a machine-readable JSON-based reporter. This
 reporter allows the test runner to be wrapped and its progress presented in
 custom ways (for example, in an IDE). See [the protocol documentation][json] for
 more details.
 
 [json]: https://github.com/dart-lang/test/blob/master/doc/json_reporter.md