in client/src/lang/parser.ts [145:160]
private field(): CqlField {
const key = this.consumeMany(
[TokenType.CHIP_KEY_POSITIVE, TokenType.CHIP_KEY_NEGATIVE],
"Expected a search key, e.g. `+tag`"
);
const maybeValue = this.safeConsume(
TokenType.CHIP_VALUE,
"Expected a search value, e.g. `+tag:new`"
);
return either(maybeValue)(
() => new CqlField(key, undefined),
(value: Token) => new CqlField(key, value)
);
}