//! Text parsers: the link/metadata extractors the text builders wrap.
//! `markdown` extracts body links; `frontmatter` extracts YAML frontmatter links
//! and the metadata block.
/// One link discovered by a parser: its raw target string as it appears in the
/// source, plus the 1-based source line where it occurs (`None` when the parser
/// cannot locate it). The builder handles normalization (fragment stripping,
/// anchor filtering, URI detection) and aggregates lines onto the edge.
/// Combined output from parsing a single file: links + optional metadata.
/// Trait implemented by the built-in text parsers.