Question: I have situation where in the regular expression is something like this:
`^b?A+b?$`

So `b` *may* match at the start of the string 0 or 1 times, and `A` *must* match one or more times. Again `b` *may* match at the end of the string 0 or 1 times.

Now I want to modify this regular expression in such way that it may match `b` either at the start or at the end of the string, but not both.

How do I do this?

Answer: 
Theres a nice "or" operator in regexps you can use.

```
^(b?A+|A+b?)$

```
```
^(b+A+b?|b?A+b+)$

```

why doesn't that work?