SAX handler forwarding all but the first start-element and last end-element event.

Note that interference with async operations (which Tokenizer is prepared to handle on start- and end-element events only, and which have been changed by Linkhandler into start-entity events at the point in the processing chain where this filter is inserted) isn't an issue with this filter (unlike Markdownoutputfilter) because the critical execution path where Tokenizer emits start-entity events (such that Outputhandler will potentially trigger asynchronous processing) will always proceed by eventually emitting start-entity events from here to nexthandler in the same synchronous execution/activation.