toAlphaOnly method
Removes all characters that are not letters (A-Z, a-z).
Implementation
String toAlphaOnly({bool allowSpace = false}) {
// Define the regex based on whether spaces are allowed.
final RegExp regExp = allowSpace ? RegExp('[^A-Za-z ]') : RegExp('[^A-Za-z]');
// Replace all non-matching characters.
return replaceAll(regExp, '');
}