diff --git a/features/bootstrap/FeatureContext.php b/features/bootstrap/FeatureContext.php
index b46de6428..aaf39713b 100644
--- a/features/bootstrap/FeatureContext.php
+++ b/features/bootstrap/FeatureContext.php
@@ -699,11 +699,15 @@ public function get_php_binary() {
 		return 'php';
 	}
 
-	public function start_php_server() {
+	public function start_php_server( $subdir = '' ) {
+		$dir = $this->variables['RUN_DIR'] . '/';
+		if ( $subdir ) {
+			$dir .= trim( $subdir, '/' ) . '/';
+		}
 		$cmd = Utils\esc_cmd( '%s -S %s -t %s -c %s %s',
 			$this->get_php_binary(),
 			'localhost:8080',
-			$this->variables['RUN_DIR'] . '/wordpress/',
+			$dir,
 			get_cfg_var( 'cfg_file_path' ),
 			$this->variables['RUN_DIR'] . '/vendor/wp-cli/server-command/router.php'
 		);
diff --git a/features/bootstrap/Process.php b/features/bootstrap/Process.php
index 8032a2415..5016580b7 100644
--- a/features/bootstrap/Process.php
+++ b/features/bootstrap/Process.php
@@ -87,15 +87,17 @@ public function run() {
 			self::$run_times[ $this->command ][1]++;
 		}
 
-		return new ProcessRun( array(
-			'stdout' => $stdout,
-			'stderr' => $stderr,
-			'return_code' => $return_code,
-			'command' => $this->command,
-			'cwd' => $this->cwd,
-			'env' => $this->env,
-			'run_time' => $run_time,
-		) );
+		return new ProcessRun(
+			array(
+				'stdout' => $stdout,
+				'stderr' => $stderr,
+				'return_code' => $return_code,
+				'command' => $this->command,
+				'cwd' => $this->cwd,
+				'env' => $this->env,
+				'run_time' => $run_time,
+			)
+		);
 	}
 
 	/**
@@ -107,7 +109,7 @@ public function run_check() {
 		$r = $this->run();
 
 		// $r->STDERR is incorrect, but kept incorrect for backwards-compat
-		if ( $r->return_code || !empty( $r->STDERR ) ) {
+		if ( $r->return_code || ! empty( $r->STDERR ) ) {
 			throw new \RuntimeException( $r );
 		}
 
diff --git a/features/bootstrap/utils.php b/features/bootstrap/utils.php
index fc8d0df84..32caac15f 100644
--- a/features/bootstrap/utils.php
+++ b/features/bootstrap/utils.php
@@ -28,9 +28,11 @@ function extract_from_phar( $path ) {
 
 	copy( $path, $tmp_path );
 
-	register_shutdown_function( function() use ( $tmp_path ) {
-		@unlink( $tmp_path );
-	} );
+	register_shutdown_function(
+		function() use ( $tmp_path ) {
+			@unlink( $tmp_path );
+		}
+	);
 
 	return $tmp_path;
 }
@@ -55,9 +57,9 @@ function load_dependencies() {
 		}
 	}
 
-	if ( !$has_autoload ) {
+	if ( ! $has_autoload ) {
 		fputs( STDERR, "Internal error: Can't find Composer autoloader.\nTry running: composer install\n" );
-		exit(3);
+		exit( 3 );
 	}
 }
 
@@ -113,7 +115,7 @@ function iterator_map( $it, $fn ) {
 		$it = new \ArrayIterator( $it );
 	}
 
-	if ( !method_exists( $it, 'add_transform' ) ) {
+	if ( ! method_exists( $it, 'add_transform' ) ) {
 		$it = new Transform( $it );
 	}
 
@@ -150,7 +152,7 @@ function find_file_upward( $files, $dir = null, $stop_check = null ) {
 		}
 
 		$parent_dir = dirname( $dir );
-		if ( empty($parent_dir) || $parent_dir === $dir ) {
+		if ( empty( $parent_dir ) || $parent_dir === $dir ) {
 			break;
 		}
 		$dir = $parent_dir;
@@ -160,8 +162,9 @@ function find_file_upward( $files, $dir = null, $stop_check = null ) {
 
 function is_path_absolute( $path ) {
 	// Windows
-	if ( isset($path[1]) && ':' === $path[1] )
+	if ( isset( $path[1] ) && ':' === $path[1] ) {
 		return true;
+	}
 
 	return $path[0] === '/';
 }
@@ -188,9 +191,13 @@ function assoc_args_to_str( $assoc_args ) {
 	foreach ( $assoc_args as $key => $value ) {
 		if ( true === $value ) {
 			$str .= " --$key";
-		} elseif( is_array( $value ) ) {
-			foreach( $value as $_ => $v ) {
-				$str .= assoc_args_to_str( array( $key => $v ) );
+		} elseif ( is_array( $value ) ) {
+			foreach ( $value as $_ => $v ) {
+				$str .= assoc_args_to_str(
+					array(
+						$key => $v,
+					)
+				);
 			}
 		} else {
 			$str .= " --$key=" . escapeshellarg( $value );
@@ -205,8 +212,9 @@ function assoc_args_to_str( $assoc_args ) {
  * returns the final command, with the parameters escaped.
  */
 function esc_cmd( $cmd ) {
-	if ( func_num_args() < 2 )
+	if ( func_num_args() < 2 ) {
 		trigger_error( 'esc_cmd() requires at least two arguments.', E_USER_WARNING );
+	}
 
 	$args = func_get_args();
 
@@ -219,15 +227,17 @@ function locate_wp_config() {
 	static $path;
 
 	if ( null === $path ) {
-		if ( file_exists( ABSPATH . 'wp-config.php' ) )
+		if ( file_exists( ABSPATH . 'wp-config.php' ) ) {
 			$path = ABSPATH . 'wp-config.php';
-		elseif ( file_exists( ABSPATH . '../wp-config.php' ) && ! file_exists( ABSPATH . '/../wp-settings.php' ) )
+		} elseif ( file_exists( ABSPATH . '../wp-config.php' ) && ! file_exists( ABSPATH . '/../wp-settings.php' ) ) {
 			$path = ABSPATH . '../wp-config.php';
-		else
+		} else {
 			$path = false;
+		}
 
-		if ( $path )
+		if ( $path ) {
 			$path = realpath( $path );
+		}
 	}
 
 	return $path;
@@ -358,7 +368,7 @@ function launch_editor_for_input( $input, $filename = 'WP-CLI' ) {
 		if ( $fp ) {
 			fclose( $fp );
 		}
-	} while( ! $tmpfile );
+	} while ( ! $tmpfile );
 
 	if ( ! $tmpfile ) {
 		\WP_CLI::error( 'Error creating temporary file.' );
@@ -368,11 +378,12 @@ function launch_editor_for_input( $input, $filename = 'WP-CLI' ) {
 	file_put_contents( $tmpfile, $input );
 
 	$editor = getenv( 'EDITOR' );
-	if ( !$editor ) {
-		if ( isset( $_SERVER['OS'] ) && false !== strpos( $_SERVER['OS'], 'indows' ) )
+	if ( ! $editor ) {
+		if ( isset( $_SERVER['OS'] ) && false !== strpos( $_SERVER['OS'], 'indows' ) ) {
 			$editor = 'notepad';
-		else
+		} else {
 			$editor = 'vi';
+		}
 	}
 
 	$descriptorspec = array( STDIN, STDOUT, STDERR );
@@ -386,8 +397,9 @@ function launch_editor_for_input( $input, $filename = 'WP-CLI' ) {
 
 	unlink( $tmpfile );
 
-	if ( $output === $input )
+	if ( $output === $input ) {
 		return false;
+	}
 
 	return $output;
 }
@@ -406,7 +418,7 @@ function mysql_host_to_cli_args( $raw_host ) {
 		if ( is_numeric( $extra ) ) {
 			$assoc_args['port'] = intval( $extra );
 			$assoc_args['protocol'] = 'tcp';
-		} else if ( $extra !== '' ) {
+		} elseif ( $extra !== '' ) {
 			$assoc_args['socket'] = $extra;
 		}
 	} else {
@@ -419,8 +431,9 @@ function mysql_host_to_cli_args( $raw_host ) {
 function run_mysql_command( $cmd, $assoc_args, $descriptors = null ) {
 	check_proc_available( 'run_mysql_command' );
 
-	if ( !$descriptors )
+	if ( ! $descriptors ) {
 		$descriptors = array( STDIN, STDOUT, STDERR );
+	}
 
 	if ( isset( $assoc_args['host'] ) ) {
 		$assoc_args = array_merge( $assoc_args, mysql_host_to_cli_args( $assoc_args['host'] ) );
@@ -435,14 +448,17 @@ function run_mysql_command( $cmd, $assoc_args, $descriptors = null ) {
 	$final_cmd = force_env_on_nix_systems( $cmd ) . assoc_args_to_str( $assoc_args );
 
 	$proc = proc_open( $final_cmd, $descriptors, $pipes );
-	if ( !$proc )
-		exit(1);
+	if ( ! $proc ) {
+		exit( 1 );
+	}
 
 	$r = proc_close( $proc );
 
 	putenv( 'MYSQL_PWD=' . $old_pass );
 
-	if ( $r ) exit( $r );
+	if ( $r ) {
+		exit( $r );
+	}
 }
 
 /**
@@ -451,14 +467,18 @@ function run_mysql_command( $cmd, $assoc_args, $descriptors = null ) {
  * IMPORTANT: Automatic HTML escaping is disabled!
  */
 function mustache_render( $template_name, $data = array() ) {
-	if ( ! file_exists( $template_name ) )
+	if ( ! file_exists( $template_name ) ) {
 		$template_name = WP_CLI_ROOT . "/templates/$template_name";
+	}
 
 	$template = file_get_contents( $template_name );
 
-	$m = new \Mustache_Engine( array(
-		'escape' => function ( $val ) { return $val; },
-	) );
+	$m = new \Mustache_Engine(
+		array(
+			'escape' => function ( $val ) {
+				return $val; },
+		)
+	);
 
 	return $m->render( $template, $data );
 }
@@ -492,8 +512,9 @@ function mustache_render( $template_name, $data = array() ) {
  * @return cli\progress\Bar|WP_CLI\NoOp
  */
 function make_progress_bar( $message, $count ) {
-	if ( \cli\Shell::isPiped() )
+	if ( \cli\Shell::isPiped() ) {
 		return new \WP_CLI\NoOp;
+	}
 
 	return new \cli\progress\Bar( $message, $count );
 }
@@ -501,7 +522,7 @@ function make_progress_bar( $message, $count ) {
 function parse_url( $url ) {
 	$url_parts = \parse_url( $url );
 
-	if ( !isset( $url_parts['scheme'] ) ) {
+	if ( ! isset( $url_parts['scheme'] ) ) {
 		$url_parts = parse_url( 'http://' . $url );
 	}
 
@@ -514,7 +535,7 @@ function parse_url( $url ) {
  * @return bool
  */
 function is_windows() {
-	return false !== ( $test_is_windows = getenv( 'WP_CLI_TEST_IS_WINDOWS' ) ) ? (bool) $test_is_windows : strtoupper(substr(PHP_OS, 0, 3)) === 'WIN';
+	return false !== ( $test_is_windows = getenv( 'WP_CLI_TEST_IS_WINDOWS' ) ) ? (bool) $test_is_windows : strtoupper( substr( PHP_OS, 0, 3 ) ) === 'WIN';
 }
 
 /**
@@ -563,23 +584,24 @@ function http_request( $method, $url, $data = null, $headers = array(), $options
 	if ( inside_phar() ) {
 		// cURL can't read Phar archives
 		$options['verify'] = extract_from_phar(
-		WP_CLI_VENDOR_DIR . $cert_path );
+			WP_CLI_VENDOR_DIR . $cert_path
+		);
 	} else {
-		foreach( get_vendor_paths() as $vendor_path ) {
+		foreach ( get_vendor_paths() as $vendor_path ) {
 			if ( file_exists( $vendor_path . $cert_path ) ) {
 				$options['verify'] = $vendor_path . $cert_path;
 				break;
 			}
 		}
-		if ( empty( $options['verify'] ) ){
-			WP_CLI::error( "Cannot find SSL certificate." );
+		if ( empty( $options['verify'] ) ) {
+			WP_CLI::error( 'Cannot find SSL certificate.' );
 		}
 	}
 
 	try {
 		$request = \Requests::request( $url, $headers, $data, $method, $options );
 		return $request;
-	} catch( \Requests_Exception $ex ) {
+	} catch ( \Requests_Exception $ex ) {
 		// CURLE_SSL_CACERT_BADFILE only defined for PHP >= 7.
 		if ( 'curlerror' !== $ex->getType() || ! in_array( curl_errno( $ex->getData() ), array( CURLE_SSL_CONNECT_ERROR, CURLE_SSL_CERTPROBLEM, 77 /*CURLE_SSL_CACERT_BADFILE*/ ), true ) ) {
 			\WP_CLI::error( sprintf( "Failed to get url '%s': %s.", $url, $ex->getMessage() ) );
@@ -589,7 +611,7 @@ function http_request( $method, $url, $data = null, $headers = array(), $options
 		$options['verify'] = false;
 		try {
 			return \Requests::request( $url, $headers, $data, $method, $options );
-		} catch( \Requests_Exception $ex ) {
+		} catch ( \Requests_Exception $ex ) {
 			\WP_CLI::error( sprintf( "Failed to get non-verified url '%s' %s.", $url, $ex->getMessage() ) );
 		}
 	}
@@ -676,7 +698,7 @@ function get_named_sem_ver( $new_version, $original_version ) {
 
 	if ( ! is_null( $minor ) && Semver::satisfies( $new_version, "{$major}.{$minor}.x" ) ) {
 		return 'patch';
-	} else if ( Semver::satisfies( $new_version, "{$major}.x.x" ) ) {
+	} elseif ( Semver::satisfies( $new_version, "{$major}.x.x" ) ) {
 		return 'minor';
 	} else {
 		return 'major';
@@ -780,7 +802,7 @@ function get_temp_dir() {
 function parse_ssh_url( $url, $component = -1 ) {
 	preg_match( '#^((docker|docker\-compose|ssh|vagrant):)?(([^@:]+)@)?([^:/~]+)(:([\d]*))?((/|~)(.+))?$#', $url, $matches );
 	$bits = array();
-	foreach( array(
+	foreach ( array(
 		2 => 'scheme',
 		4 => 'user',
 		5 => 'host',
@@ -849,17 +871,19 @@ function report_batch_operation_results( $noun, $verb, $total, $successes, $fail
  * @return array
  */
 function parse_str_to_argv( $arguments ) {
-	preg_match_all ('/(?<=^|\s)([\'"]?)(.+?)(?<!\\\\)\1(?=$|\s)/', $arguments, $matches );
+	preg_match_all( '/(?<=^|\s)([\'"]?)(.+?)(?<!\\\\)\1(?=$|\s)/', $arguments, $matches );
 	$argv = isset( $matches[0] ) ? $matches[0] : array();
-	$argv = array_map( function( $arg ){
-		foreach( array( '"', "'" ) as $char ) {
-			if ( $char === substr( $arg, 0, 1 ) && $char === substr( $arg, -1 ) ) {
-				$arg = substr( $arg, 1, -1 );
-				break;
+	$argv = array_map(
+		function( $arg ) {
+			foreach ( array( '"', "'" ) as $char ) {
+				if ( $char === substr( $arg, 0, 1 ) && $char === substr( $arg, -1 ) ) {
+					$arg = substr( $arg, 1, -1 );
+					break;
+				}
 			}
-		}
-		return $arg;
-	}, $argv );
+				return $arg;
+		}, $argv
+	);
 	return $argv;
 }
 
@@ -893,12 +917,12 @@ function basename( $path, $suffix = '' ) {
  * @return bool
  */
 function isPiped() {
-	$shellPipe = getenv('SHELL_PIPE');
+	$shellPipe = getenv( 'SHELL_PIPE' );
 
-	if ($shellPipe !== false) {
-		return filter_var($shellPipe, FILTER_VALIDATE_BOOLEAN);
+	if ( $shellPipe !== false ) {
+		return filter_var( $shellPipe, FILTER_VALIDATE_BOOLEAN );
 	} else {
-		return (function_exists('posix_isatty') && !posix_isatty(STDOUT));
+		return (function_exists( 'posix_isatty' ) && ! posix_isatty( STDOUT ));
 	}
 }
 
@@ -908,24 +932,125 @@ function isPiped() {
  * Has no effect on paths which do not use glob patterns.
  *
  * @param string|array $paths Single path as a string, or an array of paths.
- * @param int          $flags Flags to pass to glob.
+ * @param int          $flags Optional. Flags to pass to glob. Defaults to GLOB_BRACE.
  *
  * @return array Expanded paths.
  */
-function expand_globs( $paths, $flags = GLOB_BRACE ) {
+function expand_globs( $paths, $flags = 'default' ) {
+	// Compatibility for systems without GLOB_BRACE.
+	$glob_func = 'glob';
+	if ( 'default' === $flags ) {
+		if ( ! defined( 'GLOB_BRACE' ) || getenv( 'WP_CLI_TEST_EXPAND_GLOBS_NO_GLOB_BRACE' ) ) {
+			$glob_func = 'WP_CLI\Utils\glob_brace';
+		} else {
+			$flags = GLOB_BRACE;
+		}
+	}
+
 	$expanded = array();
 
 	foreach ( (array) $paths as $path ) {
 		$matching = array( $path );
 
 		if ( preg_match( '/[' . preg_quote( '*?[]{}!', '/' ) . ']/', $path ) ) {
-			$matching = glob( $path, $flags ) ?: array();
+			$matching = $glob_func( $path, $flags ) ?: array();
 		}
-
 		$expanded = array_merge( $expanded, $matching );
 	}
 
-	return array_unique( $expanded );
+	return array_values( array_unique( $expanded ) );
+}
+
+/**
+ * Simulate a `glob()` with the `GLOB_BRACE` flag set. For systems (eg Alpine Linux) built against a libc library (eg https://www.musl-libc.org/) that lacks it.
+ * Copied and adapted from Zend Framework's `Glob::fallbackGlob()` and Glob::nextBraceSub()`.
+ *
+ * Zend Framework (http://framework.zend.com/)
+ *
+ * @link      http://github.com/zendframework/zf2 for the canonical source repository
+ * @copyright Copyright (c) 2005-2015 Zend Technologies USA Inc. (http://www.zend.com)
+ * @license   http://framework.zend.com/license/new-bsd New BSD License
+ *
+ * @param string $pattern Filename pattern.
+ * @param void $dummy_flags Not used.
+ *
+ * @return array Array of paths.
+ */
+function glob_brace( $pattern, $dummy_flags = null ) {
+
+	static $next_brace_sub;
+	if ( ! $next_brace_sub ) {
+		// Find the end of the subpattern in a brace expression.
+		$next_brace_sub = function ( $pattern, $current ) {
+			$length  = strlen( $pattern );
+			$depth   = 0;
+
+			while ( $current < $length ) {
+				if ( '\\' === $pattern[ $current ] ) {
+					if ( ++$current === $length ) {
+						break;
+					}
+					$current++;
+				} else {
+					if ( ( '}' === $pattern[ $current ] && $depth-- === 0 ) || ( ',' === $pattern[ $current ] && 0 === $depth ) ) {
+						break;
+					} elseif ( '{' === $pattern[ $current++ ] ) {
+						$depth++;
+					}
+				}
+			}
+
+			return $current < $length ? $current : null;
+		};
+	}
+
+	$length = strlen( $pattern );
+
+	// Find first opening brace.
+	for ( $begin = 0; $begin < $length; $begin++ ) {
+		if ( '\\' === $pattern[ $begin ] ) {
+			$begin++;
+		} elseif ( '{' === $pattern[ $begin ] ) {
+			break;
+		}
+	}
+
+	// Find comma or matching closing brace.
+	if ( null === ( $next = $next_brace_sub( $pattern, $begin + 1 ) ) ) {
+		return glob( $pattern );
+	}
+
+	$rest = $next;
+
+	// Point `$rest` to matching closing brace.
+	while ( '}' !== $pattern[ $rest ] ) {
+		if ( null === ( $rest = $next_brace_sub( $pattern, $rest + 1 ) ) ) {
+			return glob( $pattern );
+		}
+	}
+
+	$paths = array();
+	$p = $begin + 1;
+
+	// For each comma-separated subpattern.
+	do {
+		$subpattern = substr( $pattern, 0, $begin )
+					. substr( $pattern, $p, $next - $p )
+					. substr( $pattern, $rest + 1 );
+
+		if ( ( $result = glob_brace( $subpattern ) ) ) {
+			$paths = array_merge( $paths, $result );
+		}
+
+		if ( '}' === $pattern[ $next ] ) {
+			break;
+		}
+
+		$p    = $next + 1;
+		$next = $next_brace_sub( $pattern, $p );
+	} while ( null !== $next );
+
+	return array_values( array_unique( $paths ) );
 }
 
 /**
@@ -1008,7 +1133,7 @@ function is_bundled_command( $command ) {
 	if ( null === $classes ) {
 		$classes = array();
 		$class_map = WP_CLI_VENDOR_DIR . '/composer/autoload_commands_classmap.php';
-		if ( file_exists( WP_CLI_VENDOR_DIR . '/composer/') ) {
+		if ( file_exists( WP_CLI_VENDOR_DIR . '/composer/' ) ) {
 			$classes = include $class_map;
 		}
 	}
@@ -1076,7 +1201,9 @@ function check_proc_available( $context = null, $return = false ) {
  * @return string
  */
 function past_tense_verb( $verb ) {
-	static $irregular = array( 'reset' => 'reset' );
+	static $irregular = array(
+		'reset' => 'reset',
+	);
 	if ( isset( $irregular[ $verb ] ) ) {
 		return $irregular[ $verb ];
 	}
diff --git a/features/steps/given.php b/features/steps/given.php
index e568bff3f..f2eae113f 100644
--- a/features/steps/given.php
+++ b/features/steps/given.php
@@ -211,3 +211,9 @@ function ( $world ) {
 		$world->start_php_server();
 	}
 );
+
+$steps->Given( "/^a PHP built-in web server to serve '([^\s]+)'$/",
+	function ( $world, $subdir ) {
+		$world->start_php_server( $subdir );
+	}
+);