public final void nextIdent() {
        while (isWhitespace(ch)) {
            next();
        }
        if (ch == '_' || ch == '$' || Character.isLetter(ch)) {
            scanIdent();
        } else {
            nextToken();
        }
    }
internal method, don't invoke
@param token
src/main/java/com/alibaba/fastjson/parser/JSONLexerBase.java