When using: adv_tag_group.get_all_tag_groups(server,"") this returns root groups.
adv_tag_group.get_all_tag_groups(server,".group1") this returns root groups.
adv_tag_group.get_all_tag_groups(server,".group1.") this returns group1 groups.
adv_tag_group.get_all_tag_groups(server,".group1.group2") this returns group1 groups
adv_tag_group.get_all_tag_groups(server,".group1.group2.") this returns group1 groups
Not way to get groups in group2 (eg group3) or link_tags in 'group1.group2.group3