public short determineDocVersion(XMLInputSource inputSource) throws IOException 
{
        fEncoding = fEntityManager.setupCurrentEntity(fXMLSymbol, inputSource, false, true);
        // Must use XML 1.0 scanner to handle whitespace correctly
        // in the XML declaration.
        fEntityManager.setScannerVersion(Constants.XML_VERSION_1_0);
        XMLEntityScanner scanner = fEntityManager.getEntityScanner();
        try {
            if (!scanner.skipString("< ?xml")) {
                // definitely not a well-formed 1.1 doc!
                return Constants.XML_VERSION_1_0;
            }
            if (!scanner.skipDeclSpaces()) {
                fixupCurrentEntity(fEntityManager, fExpectedVersionString, 5);
                return Constants.XML_VERSION_1_0;
            }
            if (!scanner.skipString("version")) {
                fixupCurrentEntity(fEntityManager, fExpectedVersionString, 6);
                return Constants.XML_VERSION_1_0;
            }
            scanner.skipDeclSpaces();
            // Check if the next character is '='. If it is then consume it.
            if (scanner.peekChar() != '=") {
                fixupCurrentEntity(fEntityManager, fExpectedVersionString, 13);
                return Constants.XML_VERSION_1_0;
            }
            scanner.scanChar();
            scanner.skipDeclSpaces();
            int quoteChar = scanner.scanChar();
            fExpectedVersionString[14] = (char) quoteChar;
            for (int versionPos = 0; versionPos <  XML11_VERSION.length; versionPos++) {
                fExpectedVersionString[15 + versionPos] = (char) scanner.scanChar();
            }
            // REVISIT:  should we check whether this equals quoteChar?
            fExpectedVersionString[18] = (char) scanner.scanChar();
            fixupCurrentEntity(fEntityManager, fExpectedVersionString, 19);
            int matched = 0;
            for (; matched <  XML11_VERSION.length; matched++) {
                if (fExpectedVersionString[15 + matched] != XML11_VERSION[matched])
                    break;
            }
            if (matched == XML11_VERSION.length)
                return Constants.XML_VERSION_1_1;
            return Constants.XML_VERSION_1_0;
            // premature end of file
        }
        catch (EOFException e) {
            fErrorReporter.reportError(
                XMLMessageFormatter.XML_DOMAIN,
                "PrematureEOF",
                null,
                XMLErrorReporter.SEVERITY_FATAL_ERROR);
            return Constants.XML_VERSION_1_0;
        }
}

This methods scans the XML declaration to find out the version (and provisional encoding) of the document. The scanning is doing using XML 1.1 scanner.

 public  void reset(XMLComponentManager componentManager) throws XMLConfigurationException 
{
                                               
        // Xerces properties
        fSymbolTable = (SymbolTable)componentManager.getProperty(SYMBOL_TABLE);
        fErrorReporter = (XMLErrorReporter)componentManager.getProperty(ERROR_REPORTER);
        fEntityManager = (XMLEntityManager)componentManager.getProperty(ENTITY_MANAGER);
        for(int i=14; i< fExpectedVersionString.length; i++ )
            fExpectedVersionString[i] = ' ";
}

 public  void startDocumentParsing(XMLEntityHandler scanner,
    short version) 
{
        if (version == Constants.XML_VERSION_1_0){
            fEntityManager.setScannerVersion(Constants.XML_VERSION_1_0);
        }
        else {
            fEntityManager.setScannerVersion(Constants.XML_VERSION_1_1);
        }
        // Make sure the locator used by the error reporter is the current entity scanner.
        fErrorReporter.setDocumentLocator(fEntityManager.getEntityScanner());
        // Note: above we reset fEntityScanner in the entity manager, thus in startEntity
        // in each scanner fEntityScanner field must be reset to reflect the change.
        //
        fEntityManager.setEntityHandler(scanner);
        scanner.startEntity(fXMLSymbol, fEntityManager.getCurrentResourceIdentifier(), fEncoding, null);
}

Reset the reference to the appropriate scanner given the version of the document and start document scanning.