  modify position fields.  Doing it nevertheless could
    re-enable the <code class="code">with_position</code> mode and degrade performances.</p>
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</div>
<h2 id="1_Functionsforlexersemanticactions">Functions for lexer semantic actions</h2><p>The following functions can be called from the semantic actions
   of lexer definitions (the ML code enclosed in braces that
   computes the value returned by lexing functions). They give
   access to the character string matched by the regular expression
   ass