Module step_encoding 

STEP string escape decoding/encoding (ISO 10303-21 / IFC).

IFC string attribute values encode non-ASCII characters with backslash escape sequences. This module decodes them to native UTF-8 so the Rust crates, CLI, and server surface the same text the browser parser does via decodeIfcString in @ifc-lite/encoding. The two decoders are pinned to a shared test-vector fixture (tests/fixtures/ifc_string_vectors.json).

Supported escapes:

• \X2\HHHH..\X0\ UTF-16 code units, 4 hex digits each (surrogate pairs ok)
• \X4\HHHHHHHH..\X0\ Unicode scalar values, 8 hex digits each
• \X\HH single ISO-8859-1 byte
• \S\C extended ASCII: code point of C plus 128
• \PC\ code-page directive, consumed and dropped

Unknown or malformed escapes are passed through unchanged. The '' doubled-quote escape is NOT handled here — the tokenizer’s consumers strip the surrounding quotes and un-double before calling this.

Functions

decode_ifc_string

Decode IFC STEP string escapes to UTF-8.

encode_ifc_string

Encode a UTF-8 string back to IFC STEP escapes. Inverse of decode_ifc_string for the canonical (non-overlong) forms; kept for STEP writers and round-trip tests.