Create a regex expression that excludes words containing the letter "x".
The following regex expression can be used to exclude words containing the letter "x" (case-insensitive):
```
\b((?![Xx])[a-zA-Z])+\b
```
This expression uses a negative lookahead (?!) to exclude words containing the letter "x" or "X", and the `\b` word boundaries ensure that it only matches whole words.
Complete the following task based on the instruction and optional input provided.### Instruction:
Create a regex expression that excludes words containing the letter "x".

### Output:
The following regex expression can be used to exclude words containing the letter "x" (case-insensitive):
```
\b((?![Xx])[a-zA-Z])+\b
```
This expression uses a negative lookahead (?!) to exclude words containing the letter "x" or "X", and the `\b` word boundaries ensure that it only matches whole words.