copy of the argument, with special characters represented
    by escape sequences, following the lexical conventions of OCaml.
    All characters outside the ASCII printable range (32..126) are
    escaped, as well as backslash and double-quote.</p>

<p>Raise <code class="code"><span class="constructor">Invalid_argument</span></code> if the result is longer than
    <a href="Sys.html#VALmax_string_length"><code class="code"><span class="constructor">Sys</span>.max_string_length</code></a> bytes.</p>
</div>
