Return a scene root's version string, or null when it carries none.
null
format_version (scene 0.2+) wins; the 0.1 legacy key LEGACY_SCENE_VERSION_ATTR is the fallback. Numbers are coerced to string so a numeric 0.2 still compares against the allowlist.
format_version
LEGACY_SCENE_VERSION_ATTR
0.2
Return a scene root's version string, or
nullwhen it carries none.format_version(scene 0.2+) wins; the 0.1 legacy keyLEGACY_SCENE_VERSION_ATTRis the fallback. Numbers are coerced to string so a numeric0.2still compares against the allowlist.