Sample XML:
<para0 id="p00001">
 <title>title</title>
  <warning>
   <?warningcaution MOD_A ### ID_1?>
   <para>moda id1 warning</para>
  </warning>
  <para>This is a paragraph.</para>
  <subpara1>
   <para>This is a paragraph.</para>
  </subpara1>
  <subpara1 id="sp00001">
   <title>title</title>
   <warning>
    <?warningcaution MOD_B ### ID_2?>
    <para>modb id2 warning</para>
   </warning>
   <para>This is a paragraph.</para>
  </subpara1>
  <warning>
   <?warningcaution MOD_C ### ID_3?>
   <para>modc id3 warning</para>
  </warning>
  <caution>
   <?warningcaution MOD_D ### ID_4?>
   <para>modd id4 warning</para>
  </caution>
</para0>

##</code><code>##

<para0[^>]*>\s*(?:<applic[^>]*>.*?</applic\s*>)?\s*(?:<title[^>]*>.*?</title\s*>)?\s*(?:<capgrp[^>]*>.*?</capgrp\s*>)?\s*(<warning[^>]*>\s*.*?\s*</warning\s*>)