I need some help understanding REGEXP_INSTR / SUBSTR. I got excellent assistance

here, and now I want to learn how to do it myself . . .

The pattern I'm looking for is this: M6T6W6R6, where the numbers are interspersed among the letters

- M = Mon, T = Tues, R = Thurs, etc. The numbers are class periods (1 - 10).

So I want to flag the above as "bad".

but these are good, because the numbers (periods) are not mixed in among the letters (days)

- MR567

- MTRF123456

- MF123

if this can be done, give me a tiny hint and then see if I can get it.