I have to say, that I think it’s very unfavourable, to have both, triggeringItemName and triggeringItem.name with very similar spelling.
I always have to look up very closely und use it mostly wrong, although.
Might it be an realizable idea to rename it triggeringGroupitem(.name)? Or to create it additionally?
I can image that this has a negative impact to existing configurations and rules, but sometimes it is worth to shed unnecessary load…
Please be aware that triggeringItem is a generic Item Object, while triggeringItemName is a string Object.
Furthermore, triggeringItem is only available in rules triggered by a Member of ... trigger, while triggeringItemName is only available for Item ... triggers.
In my eyes it’s not unfavorable at all, as both namings are correct and valid only in different contexts.
Please be aware that it’s not the group item which triggered, but a member of the group, so triggeringGroupitem would be wrong.