Requests that for any new node managed (eg. created) by manager, a new attribute will be set. This allows
one to customize the attributes of new nodes created by an existing #GdaTreeManager.
As a side effect, if value is null, then the corresponding attribute, if it was set, is unset.
Requests that for any new node managed (eg. created) by manager, a new attribute will be set. This allows one to customize the attributes of new nodes created by an existing #GdaTreeManager.
As a side effect, if value is null, then the corresponding attribute, if it was set, is unset.