Create a valid regular expression.
One example of a valid regular expression is `^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)[a-zA-Z\d]{8,}$`. This regular expression can be used to validate a password with the following requirements:

- At least one lowercase letter `(?=.*[a-z])`
- At least one uppercase letter `(?=.*[A-Z])`
- At least one digit `(?=.*\d)`
- A minimum length of 8 characters `.{8,}`

The `^` and `$` characters mean that the entire string must match this pattern. The `(?=...)` syntax is a positive lookahead, meaning the pattern must be matched, but won't be included in the overall match. In other words, it's a way to check that certain conditions are met, without actually capturing any characters or changing the position of the match.
Complete the following task based on the instruction and optional input provided.### Instruction:
Create a valid regular expression.

### Output:
One example of a valid regular expression is `^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)[a-zA-Z\d]{8,}$`. This regular expression can be used to validate a password with the following requirements:

- At least one lowercase letter `(?=.*[a-z])`
- At least one uppercase letter `(?=.*[A-Z])`
- At least one digit `(?=.*\d)`
- A minimum length of 8 characters `.{8,}`

The `^` and `$` characters mean that the entire string must match this pattern. The `(?=...)` syntax is a positive lookahead, meaning the pattern must be matched, but won't be included in the overall match. In other words, it's a way to check that certain conditions are met, without actually capturing any characters or changing the position of the match.