 <tr>
      <td><a href="https://wg21.link/p0400r0">P0400R0</a></td>
    </tr>
    <tr>
      <td>Requirement to ignore unknown attributes</td>
      <td><a href="https://wg21.link/p0283r2">P0283R2</a></td>
      <td class="full" align="center">Yes</td>
    </tr>
    <tr>
      <td><tt>constexpr</tt> <em>if-statement</em>s</td>
      <td><a href="https://wg21.link/p0292r2">P0292R2</a></td>
      <td class="full" align="center">Clang 3.9</td>
    </tr>
    <tr>
      <td>Inline variables</td>
      <td><a hr