def merge_data!(other, source: "YAML front matter")
      merge_categories!(other)
      Utils.deep_merge_hashes!(data, other)
      merge_date!(source)
      data
    end
def merge_data!(other, source: "YAML front matter")
      merge_categories!(other)
      Utils.deep_merge_hashes!(data, other)
      merge_date!(source)
      data
    end
Merge some data in with this document's data.

 Returns the merged data.