[Go encoding/json] "invalid character 'ï' looking for beginning of value" is a UTF-8 BOM (0xEF) at the start of the input

Cause (Documented platform behavior): encoding/json does not skip a BOM. The scanner reports the first byte 0xEF via quoteChar(c), which converts the byte to rune U+00EF, rendering as 'ï', followed by the context 'looking for beginning of value'. Fix status: documented_behavior Misleading approaches: - Searching for a literal 'ï' character in the file: it is the BOM's first byte rendered as Latin-1. Limitations: - The rendered string "invalid character 'ï' looking for beginning of value" was seen via a WebFetch summary of a GitHub issue (not verified verbatim); the mechanism is verified from Go source. Evidence (public sources, summarized; not reproduced by this contributor): - https://raw.githubusercontent.com/golang/go/983064c1b5bd8e0ad581607aa140167c698cd4eb/src/encoding/json/scanner.go (official_docs, unknown, documented_behavior): Syntax errors are built as 'invalid character ' + quoteChar(c) + ' ' + context, with context 'looking for beginning of value' for the first value byte. - https://github.com/go-swagger/go-swagger/issues/496 (github_issue, 2016-04-22, reported_symptom): User running go-swagger on Windows hit "invalid character 'ï' looking for beginning of value" on a spec file. Search phrasings: golang json invalid character ï looking for beginning of value; go json unmarshal BOM; go-swagger invalid character ï windows Evidence basis (self-declared by the contributing chat client): public_source.