I defined 2 user variables as follow:
<registers>
<register type="avalon" variable-name="allowedUsersFirstValidation">
<arg name="role">org.ametys.plugins.bpm.workflowsdef.RegisterVariable</arg>
<arg name="type">user</arg>
<arg name="multiple">true</arg>
<arg name="variableId">allowedRepresentatives</arg>
<arg name="label">plugin.default-bpm-workflow:WORKFLOW_BPM_ALLOWED_REPRESENTATIVES</arg>
<arg name="description">plugin.default-bpm-workflow:WORKFLOW_BPM_ALLOWED_REPRESENTATIVES_DESC</arg>
</register>
<register type="avalon" variable-name="allowedUsersSecondValidation">
<arg name="role">org.ametys.plugins.bpm.workflowsdef.RegisterVariable</arg>
<arg name="type">user</arg>
<arg name="multiple">true</arg>
<arg name="variableId">allowExperts</arg>
<arg name="label">plugin.default-bpm-workflow:WORKFLOW_BPM_ALLOWED_EXPERTS</arg>
<arg name="description">plugin.default-bpm-workflow:WORKFLOW_BPM_ALLOWED_EXPERTS_DESC</arg>
</register>
</registers>
When creating a workflow in BO, I can not select several users for these variable