environment.xml

<?xml version="1.0" encoding="UTF-8" ?>
<COMPATIBILITY_MATRIX>
     <PLUGIN name="qtype_stack">
         <PHP_EXTENSIONS>
             <PHP_EXTENSION name="mbstring" level="required">
                 <FEEDBACK>
                     <ON_ERROR message="mbstringrequired" plugin="qtype_stack" />
                 </FEEDBACK>
             </PHP_EXTENSION>
             <PHP_EXTENSION name="yaml" level="optional">
                 <FEEDBACK>
                     <ON_CHECK message="yamlrecommended" plugin="qtype_stack" />
                 </FEEDBACK>
             </PHP_EXTENSION>
         </PHP>
     </PLUGIN>
</COMPATIBILITY_MATRIX>