 one or more characters other than the
      <a href="terminology.html#space" id="space_xref18">space characters</a>,
      U+0000 NULL,
      "<code title="U+0022 QUOTATION MARK">"</code>",
      "<code title="U+0027 APOSTROPHE">'</code>",
      "<code title="U+003E GREATER-THAN SIGN">&gt;</code>",
      "<code title="U+002F SOLIDUS">/</code>",
      "<code title="U+003D EQUALS SIGN">=</code>",
      the control characters,
      and any characters that are not defined by Unicode.</li>
      <li>
<dfn id="