pub fn write(model: &StepModel) -> StringExpand description
Serialize the model to Part 21 text — the model’s own header
(StepModel::header, FILE_SCHEMA included) plus every entity,
verbatim.
An authored model (crate::StepBuilder / crate::Ap242Author) is
AP242 by construction and carries the AP242 schema identity, so the
output is a conforming AP242 file. A model that came from
read re-serializes faithfully under its source schema
— step-io does not convert between APs.