Which regex matches on all lowercase letters only?

Although visually similar, this option contains non-standard or improperly encoded bracket characters that would not be interpreted correctly as a regex character class by standard engines.

a*z+ matches zero or more literal 'a' characters followed by one or more literal 'z' characters, not a range of lowercase letters.

The pattern [a-z]+ defines a character class spanning all lowercase letters from 'a' to 'z' and the '+' quantifier requires one or more matches, ensuring the entire match consists solely of lowercase letters. This is the standard, correct regex syntax for this purpose.

a-z+ treats 'a-z' as a literal string sequence outside of brackets and applies '+' only to 'z', so it does not define a character class and does not match all lowercase letters.