Usda Lexical Format

usda-lexical-format

Use this skill when implementing or verifying the USDA text-format substrate.

Spec Sources

• specification/file_formats/README.md section Text

Pinned tag / commit: v1.0.1

Provides

• UTF-8 input handling
• #usda layer header parsing
• Spaces, CR/LF/CRLF, and statement separators
• Python-style and C/C++-style comments
• Single-line and multi-line strings
• Number literals including inf, -inf, and nan
• USDA identifiers
• Asset references
• Path reference delimiters

Contract

This skill owns contracts/capabilities/usda-lexical-format.json and provides the usda_lexical_format capability consumed by USDA value and spec parsing. It consumes the identifier_scanner capability from usd-identifiers-and-names for identifier validity; it should not maintain an independent UTF-8 or XID policy.

The lexer/parser substrate should preserve enough location information to emit line/column diagnostics, but exact diagnostic wording is controlled by goldens.

The substrate may be a lexer, parser-combinator layer, or direct recursive descent helpers. The contract is behavioral, not architectural.

Boundary Guards

Defer identifier UTF-8/XID scanning to usd-identifiers-and-names.

Defer path grammar after stripping angle brackets to usd-paths.

Defer value typing/coercion to usda-value-parser.

Do not map syntax to document-model fields here; that belongs to usda-spec-parser.

Test Obligations

• valid layer header
• comments in all whitespace positions
• strings and escapes
• numbers
• asset references
• invalid header diagnostic