Returns true if a token was isolated, false otherwise.
Remarks: Upon success, the delegate should return the byte-based index of the consumed pattern (tail end of it). Failure to match a pattern should be indicated by returning an Eof
Each pattern is expected to be stripped of the delimiter. An end-of-file condition causes trailing content to be placed into the token. Requests made beyond Eof result in empty matches (length is zero).
Note that additional iterator and/or reader instances will operate in lockstep when bound to a common buffer.
Iterator support.