This directory contains an altered version of the AP242 (ISO 10303-242) schema.

It is corrected to avoid the non-standard parsing requirement of the original by using explicit TREAT expression for type narrowing

Both files are identical except for a single line at line 34149 in the styled_item entity WHERE rule WR3:

Original (242_mim_lf.exp):

QUERY(it <* item | ...)

TREAT version (242_mim_lf_treat.exp):

QUERY(it <* TREAT(item AS set_representation_item) | ...)

The original AP242 schema contains a WHERE rule that:

1. Checks if item (a SELECT type) is a SET_REPRESENTATION_ITEM
2. Then tries to iterate over item in a QUERY expression

This pattern requires implicit type narrowing, which is not part of the ISO 10303-11 standard.

STEPcode implements flow-sensitive type narrowing as an extension:

• Recognizes TYPEOF guard patterns like 'Type' IN TYPEOF(var) in AND expressions
• Automatically narrows the type for subsequent uses
• Makes the original schema parse successfully

The TREAT version uses the ISO 10303-11 TREAT expression:

• TREAT(item AS set_representation_item) explicitly narrows the type
• No implicit narrowing needed
• Works in any compliant EXPRESS parser

Both versions parse successfully and produce identical output:

# Run comparison test
./test/compare_ap242_versions.sh

Expected output:

✓ Both versions parse successfully
✓ Both versions generate the same number of files

For detailed comparison, see doc/ap242-comparison.md.

• doc/ap242-comparison.md - Detailed comparison and analysis
• doc/express-type-unwrapping.md - TREAT and narrowing documentation
• src/express/test/README_AP242_BASELINE.md - Historical PE056 error info