DOCS: add comments for clarification

src/linkahead/apiutils.py

@@ -587,8 +587,10 @@ def merge_entities(entity_a: Entity,
                 raise NotImplementedError()
 
             for attribute in ("datatype", "unit", "value"):
+                # attribute is in r2
                 if (attribute in diff_r2["properties"][key] and
                         diff_r2["properties"][key][attribute] is not None):
+                    # but not in r1
                     if (attribute not in diff_r1["properties"][key] or
                             diff_r1["properties"][key][attribute] is None):
                         setattr(entity_a.get_property(key), attribute,
@@ -596,6 +598,7 @@ def merge_entities(entity_a: Entity,
                     elif force:
                         setattr(entity_a.get_property(key), attribute,
                                 diff_r2["properties"][key][attribute])
+                    # attribute in r1 but no "force"
                     else:
                         raise_error = True
                         if merge_id_with_resolved_entity is True and attribute == "value":