Editorial comments in MDI 2.1

MDI 2.1 recognizes <!-- note --> in all documents, including declared 2.0 and unversioned source. Comments can be empty, multiline or Unicode; the nearest --> closes them and their contents are not interpreted. Code, front matter, link destinations and plain-text MDI parameters remain literal. Escape an opener as \<!--.

Source saving retains comments. Default parse/prepare/mdast APIs omit them with IR 1.0; { includeComments: true } returns positional comment nodes and IR 1.1. Both report syntax 2.1. Existing front-matter declarations are retained. Public body projections and layout exclude comments even with an inclusive tree, and their source-map runs preserve the gaps.

Every publication format always omits valid comments. This intentionally changes old 2.0 output that displayed them as HTML text. Unterminated comments remain literal and return mdi.comment.unterminated: export is allowed, so intended private text may be visible.

Use source serialization or an inclusive IR for lossless comment retention. A filtered external IR cannot restore omitted comments.

Before<!-- editorial note -->after