/**	@page Exceptions Exceptions: work with errors

All exceptions in Parser have type Exception. If a problem arises,
one should throw C++ exception of that type
@code
	throw Exception("exception class",
		&string, // address of String, containing text/source of error
		"problem %d", error_code);
@endcode

"exception class" should be one of <a href="http://parser.ru/en/docs/lang/parserexceptions.htm">system</a>, 
or your own (invent a good one!), or 0.
*/