diff --git a/README.md b/README.md
index 1107ed1f..cd34859a 100644
--- a/README.md
+++ b/README.md
@@ -59,6 +59,15 @@ You can also lock it in to a specific commit or tag:
 }
 ```
 
+If you are running the libraries in a non-WordPress environment, e.g. a PHPUnit test suite that
+tests your code without loading WordPress, you'll need to polyfill the WordPress APIs used by
+the php-toolkit libraries:
+
+```php
+require_once __DIR__ . '/vendor/autoload.php';
+polyfill_wordpress_apis();
+```
+
 For now, there is no way to cherry-pick just the one library you need. It's all or nothing.
 
 Note that the composer.json example above downloads more files than the required minimum, e.g. markdowns, unit tests, the `plugins` directory, etc. That's about 50MB of code in total and, most likely, it's not a big deal for your project. If you want a smaller package, the Data Liberation plugin referenced above ships a minified phar file that's about ~500KB compressed.
diff --git a/bootstrap.php b/bootstrap.php
index 35a4af0b..36a8f90c 100644
--- a/bootstrap.php
+++ b/bootstrap.php
@@ -13,3 +13,5 @@
  */
 
 require_once __DIR__ . '/vendor/autoload.php';
+
+polyfill_wordpress_apis();
diff --git a/components/Polyfill/wordpress.php b/components/Polyfill/wordpress.php
index 5bc8773c..e365e424 100644
--- a/components/Polyfill/wordpress.php
+++ b/components/Polyfill/wordpress.php
@@ -1,222 +1,224 @@
 <?php
 /**
- * Polyfills WordPress core functions for running in non-WordPress environments
+ * Polyfills WordPress core functions to support running the php-toolkit libraries
+ * in non-WordPress environments.
  */
-
-if (
-	! isset( $html5_named_character_references ) &&
-	file_exists( __DIR__ . '/../HTML/html5-named-character-references.php' )
-) {
-	require_once __DIR__ . '/../HTML/html5-named-character-references.php';
-}
-
-if ( ! class_exists( 'WP_Block_Parser' ) ) {
-	require_once __DIR__ . '/../BlockParser/class-wp-block-parser-block.php';
-	require_once __DIR__ . '/../BlockParser/class-wp-block-parser-frame.php';
-	require_once __DIR__ . '/../BlockParser/class-wp-block-parser.php';
-}
-
-if ( ! function_exists( '_doing_it_wrong' ) ) {
-	$GLOBALS['_doing_it_wrong_messages'] = array();
-	function _doing_it_wrong( $method, $message, $version ) {
-		$GLOBALS['_doing_it_wrong_messages'][] = $message;
+function polyfill_wordpress_apis() {
+	if (
+		! isset( $html5_named_character_references ) &&
+		file_exists( __DIR__ . '/../HTML/html5-named-character-references.php' )
+	) {
+		require_once __DIR__ . '/../HTML/html5-named-character-references.php';
 	}
-}
 
-if ( ! class_exists( 'WP_Exception' ) ) {
-	class WP_Exception extends Exception {
+	if ( ! class_exists( 'WP_Block_Parser' ) ) {
+		require_once __DIR__ . '/../BlockParser/class-wp-block-parser-block.php';
+		require_once __DIR__ . '/../BlockParser/class-wp-block-parser-frame.php';
+		require_once __DIR__ . '/../BlockParser/class-wp-block-parser.php';
 	}
-}
 
-if ( ! function_exists( 'wp_trigger_error' ) ) {
-	function wp_trigger_error( $function_name, $message, $error_level = E_USER_NOTICE ) {
-		if ( ! empty( $function_name ) ) {
-			$message = sprintf( '%s(): %s', $function_name, $message );
+	if ( ! function_exists( '_doing_it_wrong' ) ) {
+		$GLOBALS['_doing_it_wrong_messages'] = array();
+		function _doing_it_wrong( $method, $message, $version ) {
+			$GLOBALS['_doing_it_wrong_messages'][] = $message;
 		}
+	}
 
-		if ( E_USER_ERROR === $error_level ) {
-			throw new WP_Exception( $message );
+	if ( ! class_exists( 'WP_Exception' ) ) {
+		class WP_Exception extends Exception {
 		}
-
-		trigger_error( $message, $error_level );
 	}
-}
 
-if ( ! function_exists( 'wp_kses_uri_attributes' ) ) {
-	function wp_kses_uri_attributes() {
-		return array();
-	}
-}
+	if ( ! function_exists( 'wp_trigger_error' ) ) {
+		function wp_trigger_error( $function_name, $message, $error_level = E_USER_NOTICE ) {
+			if ( ! empty( $function_name ) ) {
+				$message = sprintf( '%s(): %s', $function_name, $message );
+			}
 
-if ( ! function_exists( '__' ) ) {
-	function __( $input ) {
-		return $input;
-	}
-}
+			if ( E_USER_ERROR === $error_level ) {
+				throw new WP_Exception( $message );
+			}
 
-if ( ! function_exists( 'esc_attr' ) ) {
-	function esc_attr( $input ) {
-		return htmlspecialchars( $input );
+			trigger_error( $message, $error_level );
+		}
 	}
-}
 
-if ( ! function_exists( 'esc_html' ) ) {
-	function esc_html( $input ) {
-		return htmlspecialchars( $input );
+	if ( ! function_exists( 'wp_kses_uri_attributes' ) ) {
+		function wp_kses_uri_attributes() {
+			return array();
+		}
 	}
-}
 
-if ( ! function_exists( 'esc_url' ) ) {
-	function esc_url( $url ) {
-		return htmlspecialchars( $url );
+	if ( ! function_exists( '__' ) ) {
+		function __( $input ) {
+			return $input;
+		}
 	}
-}
 
-if ( ! function_exists( 'add_filter' ) ) {
-	function add_filter( $hook_name, $callback, $priority = 10, $accepted_args = 1 ) {
-		global $wp_filter;
-		if ( ! isset( $wp_filter ) ) {
-			$wp_filter = array();
-		}
-		if ( ! isset( $wp_filter[ $hook_name ] ) ) {
-			$wp_filter[ $hook_name ] = array();
-		}
-		if ( ! isset( $wp_filter[ $hook_name ][ $priority ] ) ) {
-			$wp_filter[ $hook_name ][ $priority ] = array();
+	if ( ! function_exists( 'esc_attr' ) ) {
+		function esc_attr( $input ) {
+			return htmlspecialchars( $input );
 		}
-		$wp_filter[ $hook_name ][ $priority ][] = array(
-			'function'      => $callback,
-			'accepted_args' => $accepted_args,
-		);
-
-		return true;
 	}
-}
 
-if ( ! function_exists( 'add_action' ) ) {
-	function add_action( $hook_name, $callback, $priority = 10, $accepted_args = 1 ) {
-		return add_filter( $hook_name, $callback, $priority, $accepted_args );
+	if ( ! function_exists( 'esc_html' ) ) {
+		function esc_html( $input ) {
+			return htmlspecialchars( $input );
+		}
 	}
-}
 
-if ( ! function_exists( 'apply_filters' ) ) {
-	function apply_filters( $hook_name, $value ) {
-		global $wp_filter;
-		if ( ! isset( $wp_filter[ $hook_name ] ) ) {
-			return $value;
+	if ( ! function_exists( 'esc_url' ) ) {
+		function esc_url( $url ) {
+			return htmlspecialchars( $url );
 		}
-		$args = func_get_args();
-		array_shift( $args ); // Remove hook name
+	}
 
-		ksort( $wp_filter[ $hook_name ] );
-		foreach ( $wp_filter[ $hook_name ] as $priority => $functions ) {
-			foreach ( $functions as $function ) {
-				$args[0] = $value;
-				$value   = call_user_func_array( $function['function'], array_slice( $args, 0, $function['accepted_args'] ) );
+	if ( ! function_exists( 'add_filter' ) ) {
+		function add_filter( $hook_name, $callback, $priority = 10, $accepted_args = 1 ) {
+			global $wp_filter;
+			if ( ! isset( $wp_filter ) ) {
+				$wp_filter = array();
+			}
+			if ( ! isset( $wp_filter[ $hook_name ] ) ) {
+				$wp_filter[ $hook_name ] = array();
+			}
+			if ( ! isset( $wp_filter[ $hook_name ][ $priority ] ) ) {
+				$wp_filter[ $hook_name ][ $priority ] = array();
 			}
+			$wp_filter[ $hook_name ][ $priority ][] = array(
+				'function'      => $callback,
+				'accepted_args' => $accepted_args,
+			);
+
+			return true;
 		}
+	}
 
-		return $value;
+	if ( ! function_exists( 'add_action' ) ) {
+		function add_action( $hook_name, $callback, $priority = 10, $accepted_args = 1 ) {
+			return add_filter( $hook_name, $callback, $priority, $accepted_args );
+		}
 	}
-}
 
-if ( ! function_exists( 'do_action' ) ) {
-	function do_action( $hook_name ) {
-		global $wp_filter;
-		if ( ! isset( $wp_filter[ $hook_name ] ) ) {
-			return;
+	if ( ! function_exists( 'apply_filters' ) ) {
+		function apply_filters( $hook_name, $value ) {
+			global $wp_filter;
+			if ( ! isset( $wp_filter[ $hook_name ] ) ) {
+				return $value;
+			}
+			$args = func_get_args();
+			array_shift( $args ); // Remove hook name
+
+			ksort( $wp_filter[ $hook_name ] );
+			foreach ( $wp_filter[ $hook_name ] as $priority => $functions ) {
+				foreach ( $functions as $function ) {
+					$args[0] = $value;
+					$value   = call_user_func_array( $function['function'], array_slice( $args, 0, $function['accepted_args'] ) );
+				}
+			}
+
+			return $value;
 		}
-		$args = func_get_args();
-		array_shift( $args ); // Remove hook name
+	}
 
-		ksort( $wp_filter[ $hook_name ] );
-		foreach ( $wp_filter[ $hook_name ] as $priority => $functions ) {
-			foreach ( $functions as $function ) {
-				call_user_func_array( $function['function'], array_slice( $args, 0, $function['accepted_args'] ) );
+	if ( ! function_exists( 'do_action' ) ) {
+		function do_action( $hook_name ) {
+			global $wp_filter;
+			if ( ! isset( $wp_filter[ $hook_name ] ) ) {
+				return;
+			}
+			$args = func_get_args();
+			array_shift( $args ); // Remove hook name
+
+			ksort( $wp_filter[ $hook_name ] );
+			foreach ( $wp_filter[ $hook_name ] as $priority => $functions ) {
+				foreach ( $functions as $function ) {
+					call_user_func_array( $function['function'], array_slice( $args, 0, $function['accepted_args'] ) );
+				}
 			}
 		}
 	}
-}
 
-if ( ! function_exists( 'parse_blocks' ) ) {
-	function parse_blocks( $input ) {
-		$parser = new WP_Block_Parser();
+	if ( ! function_exists( 'parse_blocks' ) ) {
+		function parse_blocks( $input ) {
+			$parser = new WP_Block_Parser();
 
-		return $parser->parse( $input );
+			return $parser->parse( $input );
+		}
 	}
-}
 
-if ( ! function_exists( 'serialize_blocks' ) ) {
-	function serialize_blocks( $blocks ) {
-		return implode( '', array_map( 'serialize_block', $blocks ) );
+	if ( ! function_exists( 'serialize_blocks' ) ) {
+		function serialize_blocks( $blocks ) {
+			return implode( '', array_map( 'serialize_block', $blocks ) );
+		}
 	}
-}
 
-if ( ! function_exists( 'serialize_block' ) ) {
-	function serialize_block( $block ) {
-		$block_content = '';
+	if ( ! function_exists( 'serialize_block' ) ) {
+		function serialize_block( $block ) {
+			$block_content = '';
 
-		$index = 0;
-		foreach ( $block['innerContent'] as $chunk ) {
-			$block_content .= is_string( $chunk ) ? $chunk : serialize_block( $block['innerBlocks'][ $index ++ ] );
-		}
+			$index = 0;
+			foreach ( $block['innerContent'] as $chunk ) {
+				$block_content .= is_string( $chunk ) ? $chunk : serialize_block( $block['innerBlocks'][ $index ++ ] );
+			}
 
-		if ( ! is_array( $block['attrs'] ) ) {
-			$block['attrs'] = array();
-		}
+			if ( ! is_array( $block['attrs'] ) ) {
+				$block['attrs'] = array();
+			}
 
-		return get_comment_delimited_block_content(
-			$block['blockName'],
-			$block['attrs'],
-			$block_content
-		);
+			return get_comment_delimited_block_content(
+				$block['blockName'],
+				$block['attrs'],
+				$block_content
+			);
+		}
 	}
-}
 
-if ( ! function_exists( 'get_comment_delimited_block_content' ) ) {
-	function get_comment_delimited_block_content( $block_name, $block_attributes, $block_content ) {
-		if ( is_null( $block_name ) ) {
-			return $block_content;
-		}
+	if ( ! function_exists( 'get_comment_delimited_block_content' ) ) {
+		function get_comment_delimited_block_content( $block_name, $block_attributes, $block_content ) {
+			if ( is_null( $block_name ) ) {
+				return $block_content;
+			}
 
-		$serialized_block_name = strip_core_block_namespace( $block_name );
-		$serialized_attributes = empty( $block_attributes ) ? '' : serialize_block_attributes( $block_attributes ) . ' ';
+			$serialized_block_name = strip_core_block_namespace( $block_name );
+			$serialized_attributes = empty( $block_attributes ) ? '' : serialize_block_attributes( $block_attributes ) . ' ';
 
-		if ( empty( $block_content ) ) {
-			return sprintf( '<!-- wp:%s %s/-->', $serialized_block_name, $serialized_attributes );
-		}
+			if ( empty( $block_content ) ) {
+				return sprintf( '<!-- wp:%s %s/-->', $serialized_block_name, $serialized_attributes );
+			}
 
-		return sprintf(
-			'<!-- wp:%s %s-->%s<!-- /wp:%s -->',
-			$serialized_block_name,
-			$serialized_attributes,
-			$block_content,
-			$serialized_block_name
-		);
+			return sprintf(
+				'<!-- wp:%s %s-->%s<!-- /wp:%s -->',
+				$serialized_block_name,
+				$serialized_attributes,
+				$block_content,
+				$serialized_block_name
+			);
+		}
 	}
-}
 
-if ( ! function_exists( 'strip_core_block_namespace' ) ) {
-	function strip_core_block_namespace( $block_name = null ) {
-		if ( is_string( $block_name ) && strncmp( $block_name, 'core/', strlen( 'core/' ) ) === 0 ) {
-			return substr( $block_name, 5 );
-		}
+	if ( ! function_exists( 'strip_core_block_namespace' ) ) {
+		function strip_core_block_namespace( $block_name = null ) {
+			if ( is_string( $block_name ) && strncmp( $block_name, 'core/', strlen( 'core/' ) ) === 0 ) {
+				return substr( $block_name, 5 );
+			}
 
-		return $block_name;
+			return $block_name;
+		}
 	}
-}
 
 
-if ( ! function_exists( 'serialize_block_attributes' ) ) {
-	function serialize_block_attributes( $block_attributes ) {
-		$encoded_attributes = json_encode( $block_attributes, JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE );
-		$encoded_attributes = preg_replace( '/--/', '\\u002d\\u002d', $encoded_attributes );
-		$encoded_attributes = preg_replace( '/</', '\\u003c', $encoded_attributes );
-		$encoded_attributes = preg_replace( '/>/', '\\u003e', $encoded_attributes );
-		$encoded_attributes = preg_replace( '/&/', '\\u0026', $encoded_attributes );
-		// Regex: /\\"/
-		$encoded_attributes = preg_replace( '/\\\\"/', '\\u0022', $encoded_attributes );
+	if ( ! function_exists( 'serialize_block_attributes' ) ) {
+		function serialize_block_attributes( $block_attributes ) {
+			$encoded_attributes = json_encode( $block_attributes, JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE );
+			$encoded_attributes = preg_replace( '/--/', '\\u002d\\u002d', $encoded_attributes );
+			$encoded_attributes = preg_replace( '/</', '\\u003c', $encoded_attributes );
+			$encoded_attributes = preg_replace( '/>/', '\\u003e', $encoded_attributes );
+			$encoded_attributes = preg_replace( '/&/', '\\u0026', $encoded_attributes );
+			// Regex: /\\"/
+			$encoded_attributes = preg_replace( '/\\\\"/', '\\u0022', $encoded_attributes );
 
-		return $encoded_attributes;
+			return $encoded_attributes;
+		}
 	}
 }