ordered_block

The lines between a start / end marker pair must stay sorted (and, with unique: true, free of duplicates) under comparator (lexical / lexical-ci / numeric). Both markers are optional: omit end to sort from start to EOF, omit both to sort the whole file (the markerless “this file is one sorted list” form — dictionaries, allow-lists, a fully-sorted CODEOWNERS). The generic form of per-project keep-sorted scripts (protobuf failure_lists, sorted .gitignore / CODEOWNERS / dependency lists). Per-file: with markers, a file with no start marker is silently fine; markers match the trimmed line; blank lines inside a block are ignored; one violation per out-of-order block; a fully-delimited block that never sees its end is reported unclosed (a block with an absent end runs to EOF by design). An optional select: regex restricts the sortable entries to lines matching it — other lines inside the block (comments, group headers) pass through untouched (the sectioned / keep-sorted-subset shape).

- id: keep-sorted
  kind: ordered_block
  paths: ["**/.gitignore", "CODEOWNERS"]
  start: "# keep-sorted start"
  end: "# keep-sorted end"
  comparator: lexical
  unique: false
  select: '^\s*require '   # sort only the `require '…'` lines
  level: warning

Options

Option	Type	Required	Default	Description
comparator	one of lexical | lexical-ci | numeric		lexical	Comparator used to order entries: lexical (default), lexical-ci, or numeric.
end	string		null	Marker line closing a block. Optional - omit to run the block to EOF.
select	string		null	Regex; when set, only lines inside a block matching it are sortable entries (others, such as comments or group headers, pass through). The sectioned / keep-sorted-subset shape.
start	string		null	Marker line opening a block (matched on the trimmed line). Optional - omit to anchor the block at the start of the file.
unique	boolean		false	When true, also forbid duplicate (equal) entries within a block.

Plus the common paths, level, id, and when fields. This table is generated from the JSON Schema; option types and defaults are authoritative.