xmlParseDocument(xmlParserCtxtPtr ctxt) {
    xmlChar start[4];
    xmlCharEncoding enc;

    xmlInitParser();

    if ((ctxt == NULL) || (ctxt->input == NULL))
        return(-1);

    GROW;

    /*
     * SAX: detecting the level.
     */
    xmlDetectSAX2(ctxt);

    /*
     * SAX: beginning of the document processing.
     */
    if ((ctxt->sax) && (ctxt->sax->setDocumentLocator))
        ctxt->sax->setDocumentLocator(ctxt->userData, &xmlDefaultSAXLocator);

    if ((ctxt->encoding == NULL) &&
        ((ctxt->input->end - ctxt->input->cur) >= 4)) {
	/* 
	 * Get the 4 first bytes and decode the charset
	 * if enc != XML_CHAR_ENCODING_NONE
	 * plug some encoding conversion routines.
	 */
	start[0] = RAW;
	start[1] = NXT(1);
	start[2] = NXT(2);
	start[3] = NXT(3);
	enc = xmlDetectCharEncoding(&start[0], 4);
	if (enc != XML_CHAR_ENCODING_NONE) {
	    xmlSwitchEncoding(ctxt, enc);
	}
    }


    if (CUR == 0) {
	xmlFatalErr(ctxt, XML_ERR_DOCUMENT_EMPTY, NULL);
    }

    /*
     * Check for the XMLDecl in the Prolog.
     * do not GROW here to avoid the detected encoder to decode more
     * than just the first line, unless the amount of data is really
     * too small to hold "<?xml version="1.0" encoding="foo"
     */
    if ((ctxt->input->end - ctxt->input->cur) < 35) {
       GROW;
    }
    if ((CMP5(CUR_PTR, '<', '?', 'x', 'm', 'l')) && (IS_BLANK_CH(NXT(5)))) {

	/*
	 * Note that we will switch encoding on the fly.
	 */
	xmlParseXMLDecl(ctxt);
	if (ctxt->errNo == XML_ERR_UNSUPPORTED_ENCODING) {
	    /*
	     * The XML REC instructs us to stop parsing right here
	     */
	    return(-1);
	}
	ctxt->standalone = ctxt->input->standalone;
	SKIP_BLANKS;
    } else {
	ctxt->version = xmlCharStrdup(XML_DEFAULT_VERSION);
    }
    if ((ctxt->sax) && (ctxt->sax->startDocument) && (!ctxt->disableSAX))
        ctxt->sax->startDocument(ctxt->userData);

    /*
     * The Misc part of the Prolog
     */
    GROW;
    xmlParseMisc(ctxt);

    /*
     * Then possibly doc type declaration(s) and more Misc
     * (doctypedecl Misc*)?
     */
    GROW;
    if (CMP9(CUR_PTR, '<', '!', 'D', 'O', 'C', 'T', 'Y', 'P', 'E')) {

	ctxt->inSubset = 1;
	xmlParseDocTypeDecl(ctxt);
	if (RAW == '[') {
	    ctxt->instate = XML_PARSER_DTD;
	    xmlParseInternalSubset(ctxt);
	}

	/*
	 * Create and update the external subset.
	 */
	ctxt->inSubset = 2;
	if ((ctxt->sax != NULL) && (ctxt->sax->externalSubset != NULL) &&
	    (!ctxt->disableSAX))
	    ctxt->sax->externalSubset(ctxt->userData, ctxt->intSubName,
	                              ctxt->extSubSystem, ctxt->extSubURI);
	ctxt->inSubset = 0;

        xmlCleanSpecialAttr(ctxt);

	ctxt->instate = XML_PARSER_PROLOG;
	xmlParseMisc(ctxt);
    }

    /*
     * Time to start parsing the tree itself
     */
    GROW;
    if (RAW != '<') {
	xmlFatalErrMsg(ctxt, XML_ERR_DOCUMENT_EMPTY,
		       "Start tag expected, '<' not found\n");
    } else {
	ctxt->instate = XML_PARSER_CONTENT;
	xmlParseElement(ctxt);
	ctxt->instate = XML_PARSER_EPILOG;


	/*
	 * The Misc part at the end
	 */
	xmlParseMisc(ctxt);

	if (RAW != 0) {
	    xmlFatalErr(ctxt, XML_ERR_DOCUMENT_END, NULL);
	}
	ctxt->instate = XML_PARSER_EOF;
    }

    /*
     * SAX: end of the document processing.
     */
    if ((ctxt->sax) && (ctxt->sax->endDocument != NULL))
        ctxt->sax->endDocument(ctxt->userData);

    /*
     * Remove locally kept entity definitions if the tree was not built
     */
    if ((ctxt->myDoc != NULL) &&
	(xmlStrEqual(ctxt->myDoc->version, SAX_COMPAT_MODE))) {
	xmlFreeDoc(ctxt->myDoc);
	ctxt->myDoc = NULL;
    }

    if ((ctxt->wellFormed) && (ctxt->myDoc != NULL)) {
        ctxt->myDoc->properties |= XML_DOC_WELLFORMED;
	if (ctxt->valid)
	    ctxt->myDoc->properties |= XML_DOC_DTDVALID;
	if (ctxt->nsWellFormed)
	    ctxt->myDoc->properties |= XML_DOC_NSVALID;
	if (ctxt->options & XML_PARSE_OLD10)
	    ctxt->myDoc->properties |= XML_DOC_OLD10;
    }
    if (! ctxt->wellFormed) {
	ctxt->valid = 0;
	return(-1);
    }
    return(0);
}