Assemble imported sequence-item scopes

docs/config.md

@@ -884,6 +884,25 @@ walk failures, matched directories, invalid documents, escapes, and repeated tar
 remain errors. Final candidates are bounded by the remaining source limit before
 their contents are accumulated.
 
+Each path or glob declaration may include `placement: mapping` or
+`placement: sequence-item`. Omission means `mapping` for that declaration,
+including every match of a glob; placement is not inherited. Sequence-item
+placement requires a nonempty effective destination and wraps the imported
+mapping as one element of a sequence there. It does not split source sequences
+or enable sequence accumulation: overlapping sequences still follow the strict
+composition rules above.
+
+An item import first opens a local mapping scope. Its body and ordinary helper
+imports compose within that record. An omitted helper destination or
+`destination: []` places the helper at the record root; other destinations are
+relative to the immediate importing source. A helper may supply fields such as
+the record's `id`. An explicit nested `sequence-item` import creates a sequence
+inside the record, and its placement is independent of the enclosing item.
+At the record root, an item import must name a nonempty nested destination.
+Physical paths continue to resolve from the file that declares each import.
+An actual empty mapping contributes an empty item, while an optional unmatched
+path or glob contributes nothing.
+
 For host files, the configuration root defaults to the selected file's canonical
 directory. A host file may supply `FilesystemContext.Root` to widen that root but
 may not supply `BaseDir` or a native `FS`. Byte, reader, and mapping inputs with host context