Abstract syntax tree source location

An abstract syntax tree can retain source locations even while omitting punctuation nodes. Python records one-based line numbers and zero-based UTF-8 byte offsets, with the end offset exclusive. In x=2+3*4, the multiplication node spans offsets $4$ through $7$, and ast.get_source_segment returns 3*4. A copied location on a folded 12 describes the original span, not text newly present in the source. Such metadata supports error messages and editing tools without making an abstract syntax tree a lossless record of formatting. ^[ref]

// Target: computer-science.bigb