Function wire_begin_string 

pub fn wire_begin_string(version: &str) -> &str

SUITE_VERSIONS’ "FIX.Latest" entry is a version-agnostic-testing label, not a real wire BeginString (feature 007, BUG-79/FR-048’s stricter frame_length format check would otherwise reject it outright, unlike every real value in SUITE_VERSIONS) — this maps it to a real, well-formed BeginString for anywhere actual wire bytes get constructed, leaving every other version untouched. The bundled FIXLATEST dictionary’s own .version field is a separate, unrelated label (only ever compared via version_meta, which no bundled dictionary populates) — not affected by this translation.