XML

omnist::formats::xml::{read_xml, write_xml, check_xml}. Ported from ~/dev/omnist/omnist/formats.py’s read_xml/write_xml/check_xml; see omnist/src/formats/xml.rs’s module doc for the full detail.

XML needs exactly one document element, so (unlike JSON/YAML/TOML) an example document must be wrapped under a single top-level element.

#![allow(unused)]
fn main() {
use indexmap::IndexMap;
use omnist::document::{Doc, Value};
use omnist::formats::xml::{read_xml, write_xml};

let mut fields = IndexMap::new();
fields.insert("name".to_string(), Value::Str("Ada".to_string()));
fields.insert("age".to_string(), Value::Int(37));
let mut root = IndexMap::new();
root.insert("person".to_string(), Value::Object(fields));
let doc = Doc::of(&Value::Object(root)).unwrap();

let text = write_xml(&doc, true, None).unwrap();
let doc2 = read_xml(&text).unwrap();
assert!(doc.eq_doc(&doc2));
}

Structural difference: interleaving-preserving, not grouped

Unlike the other three codecs, this module goes through Doc::from_raw/ Doc::to_raw (RawNode), not Doc::to_grouped – XML element order can interleave distinct labels arbitrarily (<b/><c/><b/>), which a JSON-shaped IndexMap can’t represent.

quick-xml: no advisory, no DTD/entity-expansion at all

cargo audit against this crate’s full dependency tree (29 crates, including quick-xml 0.41.0) on 2026-07-26 against the RustSec advisory database found zero matches – unlike TS’s port, which carried an unfixable fast-xml-parser advisory (omnist-ts#38). quick-xml also has no DTD/external-entity expansion support at all (only the five predefined XML entities are recognized; an undefined entity is a parse error) – XXE -safe by construction, not by configuration (Python’s read_xml needs defusedxml instead of the stdlib ElementTree for the same protection).

Namespaces: a disclosed simplification

quick_xml runs in non-namespace-aware mode here; a namespaced tag’s local name is taken by stripping a lexical prefix: up to the last :, which coincides with Python’s ElementTree-based behavior for the common case (a declared, in-scope prefix) but does not resolve prefixes through xmlns declarations. Namespaces are outside this issue’s spec.

Scalar coercion, live-checked against Python’s _coerce

Confirmed against a live Python interpreter, not assumed:

• The empty string reads as "", never coerced.
• A case-insensitive, whole-string, untrimmed match against "true"/"false" reads as a bool – " true " (with surrounding whitespace) stays a string.
• Otherwise int(text) is tried, then float(text), both after Python-style trimming and accepting a single _ between two digits as a group separator ("1_0" -> 10); text that matches neither stays a string.
• float(text) also accepts inf/infinity/nan (any case, optionally signed).
• Disclosed representational gap: this port’s Scalar::Int is i64-backed (max ~19 digits); Python’s int is arbitrary-precision. Text between 20 and 4300 digits that Python holds as an exact int falls through here to Scalar::Float instead (the same int-then-float fallback order Python’s _coerce itself uses, not a new divergence).
• Not replicated: Python’s int()/float() accept any Unicode decimal digit (e.g. Arabic-Indic digits); this module’s parsers are ASCII-digit-only – a disclosed, narrower-than-Python simplification.