Listener for messages from the HTML parser.
The classification of problems as warnings or errors is the one of the HTML parser
used by HtmlUnit. The line and column may indicates the position of the problem detected
by the parser. This is only an indication and in some cases the position where
the problem has to be solved is located lines before.
In some cases (when parsing a html snippet), the html content is also available.
Simple implementation of HTMLParserListener logging the received warnings
and errors in the "com.gargoylesoftware.htmlunit.html.HTMLParserListener" log.
Errors are logged at the error level and warnings at the warning level.