diff --git a/includes/XmlTypeCheck.php b/includes/XmlTypeCheck.php
index 2062101..761ba6a 100644
--- a/includes/XmlTypeCheck.php
+++ b/includes/XmlTypeCheck.php
@@ -53,10 +53,14 @@ class XmlTypeCheck {
 	 * @param array $options list of additional parsing options:
 	 *	processing_instruction_handler: Callback for xml_set_processing_instruction_handler
 	 */
-	function __construct( $file, $filterCallback=null, $options=array() ) {
+	function __construct( $file, $filterCallback=null, $options=array(), $isFile = true ) {
 		$this->filterCallback = $filterCallback;
 		$this->parserOptions = array_merge( $this->parserOptions, $options );
+		if ( $isFile ) {
 			$this->run( $file );
+		} else {
+			$this->validateFromString( $file );
+		}
 	}
 
 	/**
@@ -110,6 +114,40 @@ class XmlTypeCheck {
 	}
 
 	/**
+	 * Get an XML parser with the root element handler.
+	 * @see XmlTypeCheck::rootElementOpen()
+	 * @return resource a resource handle for the XML parser
+	 */
+	private function getParser() {
+		$parser = xml_parser_create_ns( 'UTF-8' );
+		// case folding violates XML standard, turn it off
+		xml_parser_set_option( $parser, XML_OPTION_CASE_FOLDING, false );
+		xml_set_element_handler( $parser, array( $this, 'rootElementOpen' ), false );
+		if ( $this->parserOptions['processing_instruction_handler'] ) {
+			xml_set_processing_instruction_handler(
+				$parser,
+				array( $this, 'processingInstructionHandler' )
+			);
+		}
+		return $parser;
+	}
+
+	/**
+	 *
+	 * @param string $string the XML-input-string to be checked.
+	 */
+	private function validateFromString( $string ) {
+		$parser = $this->getParser();
+		$ret = xml_parse( $parser, $string, true );
+		xml_parser_free( $parser );
+		if ( $ret == 0 ) {
+			$this->wellFormed = false;
+			return;
+		}
+		$this->wellFormed = true;
+	}
+
+	/**
 	 * @param $parser
 	 * @param $name
 	 * @param $attribs
diff --git a/tests/phpunit/includes/upload/UploadTest.php b/tests/phpunit/includes/upload/UploadTest.php
index ad1bc72..42b0a0b 100644
--- a/tests/phpunit/includes/upload/UploadTest.php
+++ b/tests/phpunit/includes/upload/UploadTest.php
@@ -368,8 +368,8 @@ class UploadTestHandler extends UploadBase {
 		$check = new XmlTypeCheck(
 			$svg,
 			array( $this, 'checkSvgScriptCallback' ),
-			false,
-			array( 'processing_instruction_handler' => 'UploadBase::checkSvgPICallback' )
+			array( 'processing_instruction_handler' => 'UploadBase::checkSvgPICallback' ),
+			false
 		);
 		return array( $check->wellFormed, $check->filterMatch );
 	}