presto-parser/src/main/java/io/prestosql/sql/parser/AstBuilder.java/AstBuilder/isValidUnicodeEscape
class AstBuilder:    private static boolean isValidUnicodeEscape(char c)
    {
        return c < 0x7F && c > 0x20 && !isHexDigit(c) && c != '"' && c != '+' && c != '\'';
    }