t state of the scanner, plus
   a function to refill the buffer from the input.</p>

<p>Lexers can optionally maintain the <code class="code">lex_curr_p</code> and <code class="code">lex_start_p</code>
   position fields.  This "position tracking" mode is the default, and
   it corresponds to passing <code class="code">~with_position:true</code> to functions that
   create lexer buffers. In this mode, the lexing engine and lexer
   actions are co-responsible for properly updating the position
   fields, as 