Function is_length_prefixed 

fn is_length_prefixed(key: u64) -> bool

Whether a Table 7 parameter’s value carries its own length prefix.

The four nestable Range Filters (0x25 through 0x28). FILL_TIMEOUT (0x0A) is the only bare varint in the table, and LOCATION_FILTER (0x21) is neither: its value is a Location Filter Type and the fields that type names, with no length ahead of them, nested or not.