# Render formatting
ComposeLens separates merged-project semantics from YAML presentation. `render_canonical` always
uses the fixed canonical-v2 format. `render_canonical_with_formatting` accepts explicit
presentation-only choices while producing the same YAML data model.
## Available choices
| Indentation width | two spaces | any positive `u8` number of spaces |
| Line ending | LF | LF or CRLF |
| YAML document marker | emitted | emit or omit `---` |
| Final line ending | emitted | emit or omit |
```rust
use compose_lens::render::{CanonicalFormatting, IndentWidth, LineEnding};
let formatting = CanonicalFormatting::default()
.with_indent_width(IndentWidth::new(4).expect("four is nonzero"))
.with_line_ending(LineEnding::CrLf)
.with_document_marker(true)
.with_final_newline(false);
assert_eq!(formatting.indent_width().spaces(), 4);
assert_eq!(formatting.line_ending(), LineEnding::CrLf);
assert!(formatting.document_marker());
assert!(!formatting.final_newline());
```
Pass this value to `render_canonical_with_formatting` together with the same merged project and
optional profile selection accepted by `render_canonical`.
## Options that deliberately do not exist
Formatting cannot:
- interpolate environment variables;
- merge Compose documents;
- select profiles;
- resolve paths or apply defaults;
- sort mappings or services;
- normalize or interchange short and long Compose forms;
- validate provider/runtime compatibility; or
- invoke Docker, Podman, or another process.
String and key quoting is deterministic and minimal: ComposeLens emits a plain scalar only after
it parses back as one plain YAML string. Ambiguous YAML 1.1 boolean/null, sexagesimal, special
floating-point, date, and timestamp spellings remain quoted.
Mapping and sequence order remains the order of the merged semantic model.
## Canonical versus customized output
The default is named `compose-lens-canonical-v2` for exact fixture comparison. Customized
output remains deterministic for the same project, selection, and formatting value, and it must
parse to the same semantic model. Use canonical-v2 when stable shared bytes are more important than
repository-specific presentation.
Formatting options do not apply to preservation-oriented edits. Those edits retain all authored
bytes outside their exact target spans. ADR 0011 defines the [formatting boundary](decisions/0011-presentation-only-render-formatting.md).