by the generated scanners.
   The lexer buffer holds the current state of the scanner, plus
   a function to refill the buffer from the input.</p>

<p>At each token, the lexing engine will copy <code class="code">lex_curr_p</code> to
   <code class="code">lex_start_p</code>, then change the <code class="code">pos_cnum</code> field
   of <code class="code">lex_curr_p</code> by updating it with the number of characters read
   since the start of the <code class="code">lexbuf</code>.  The other fields are left