The NBT path parser used by /data get|remove and /execute store result|success entity|block might be too lenient. It does not require the path piece separator . (period) between pieces and the separator can be repeated multiple times.
This allows constructs like the following:
Keys would always require quotation marks, list indices would just be the index.
When parsing, a strings would be treated as compound keys and integers as list indices. The separator would be required.
In my opinion a slash (or other taller characters) make it easier to see the distinguish path pieces.