title: Parsing cases that need much lookahead
body: <p>Most parsing can be done by looking only at the next symbol (character for lexical analysis, token for parsing proper), and most of the remaining cases can be handled by looking at only one symbol after that.</p>
  
  <p>Are there any practical cases - for programming languages or data formats in actual use - that need several or indefinitely many symbols of lookahead (or equivalently backtracking)?</p>