Function merge_named_ranges 

pub fn merge_named_ranges(
    doc: &mut AutoCommit,
    record_ids: &[String],
    start: &HistoryEntryId,
    end: Option<&HistoryEntryId>,
    label: &str,
) -> Option<String>

Merge named bands into one caller-resolved range. Every old record must exist before anything is changed, so a stale UI cannot partially merge a set that a collaborator has already edited.