usedTokens property
UsedTokens is what the returned spans actually cost, by the same estimate the packer used (roughly one token per four characters — an estimate, not a tokenizer's count, so size a real window with headroom).
Please note: This property should have been non-nullable! Since the specification file does not include a default value (using the "default:" property), however, the generated source code must fall back to having a nullable type. Consider adding a "default:" property in the specification file to hide this note.
Implementation
int? usedTokens;