Function sp_state_machine::key_changes

pub fn key_changes<'a, H: Hasher, Number: BlockNumber>(
    config: ConfigurationRange<'a, Number>, 
    storage: &'a dyn Storage<H, Number>, 
    begin: Number, 
    end: &'a AnchorBlockId<H::Out, Number>, 
    max: Number, 
    storage_key: Option<&'a PrefixedStorageKey>, 
    key: &'a [u8]
) -> Result<DrilldownIterator<'a, H, Number>, String>

Return changes of given key at given blocks range. max is the number of best known block. Changes are returned in descending order (i.e. last block comes first).