Function detect_front_matter 

pub fn detect_front_matter(
    content: &str,
) -> Option<(FrontMatterFormat, &str, usize)>

Locates the front-matter block without parsing it.

Returns the format, the raw block, and the byte offset at which the document body begins. Detection order is YAML, TOML, JSON, the same order extract_metadata uses; None means no shape matched.

Example

use metadata_gen::metadata::{detect_front_matter, FrontMatterFormat};

let doc = "---\ntitle: T\n---\nBody";
let (format, raw, body_start) = detect_front_matter(doc).unwrap();
assert_eq!(format, FrontMatterFormat::Yaml);
assert_eq!(raw, "title: T");
assert_eq!(&doc[body_start..], "Body");