The widget TagSelect is applicable to a relationship O2M like M2M and allows you to select multiple records on the fly and create a new record using the current value of the search box field. Since a record can have several required fields, they must be explained and thus are mapped to the current value of the search field.
For example, the entity com.axelor.auth.db.User has three required fields: code , name and password . On the fly to create a record with the value for the required fields, the current value of the search field, here is the syntax:
<field name="members" widget="TagSelect[create=code,name,password]"/>