Also using Word(-1,...) might be enough if your strings are simple enough
Names Default To Here(1);
str1 = "Plate[QWE147] Reg[ABC123]";
str2 = "Plate[ASD258] Reg[DEF456]";
Show(Word(-1, str1, "[]")); // Word(-1, str1, "[]") = "ABC123";
Show(Word(-1, str2, "[]")); // Word(-1, str2, "[]") = "DEF456";
-Jarmo