build method
Returns object which might be used to execute processing tree.
If xml fail to parse, then XmlParserException
is thrown. If xml is
valid but it's unable to build tree then TreeBuilderException is thrown,
otherwise ready to use implementation of TreeProcessor is returned.
Implementation
TreeProcessor build(String xmlStr) {
_parseXml(xmlStr);
if (_processor == null) {
throw TreeBuilderException("Unable to build tree.");
}
return _processor!;
}