extension PureYAML.Parsing {
    enum ScannerFlowContextKind {
        case sequence
        case mapping
    }

    struct ScannerFlowContext {
        var kind: ScannerFlowContextKind
        var isExpectingKey: Bool
    }

    /// A position that may be promoted to a flow-mapping key, mirroring libyaml's
    /// `yaml_simple_key_t`. When a `:` value indicator is later found, the scanner
    /// inserts a ``TokenKind/mappingKey`` token at ``tokenIndex`` so a node of any
    /// kind (plain or quoted scalar, or a nested `[...]`/`{...}` collection) that
    /// precedes the `:` becomes that pair's key. Only used inside flow collections;
    /// block context promotes keys with a forward lookahead instead.
    struct ScannerFlowSimpleKey {
        var tokenIndex: Int
        var mark: PureYAML.Parsing.Mark
    }
}