Constant CON_SPEC_VERSION 

pub const CON_SPEC_VERSION: u32 = 3;

CON/convel format spec version implemented by this build.

• Version 1: column 5 present but semantics undefined. Readers MAY ignore it. No JSON metadata line.
• Version 2: column 5 is the original atom index before type-based grouping; JSON line 2 with at least {"con_spec_version": 2}.
• Version 3: same as v2 plus required metadata["units"] object with non-empty length and energy unit strings (see units module).

See docs/orgmode/spec.org for the full specification.