Which statement is true regarding string datatypes?

String data types are versatile and can hold a sequence of characters, which may include letters, digits, symbols, and even whitespace. One of the key features of string data types is their ability to store data in varying lengths, meaning that they can accommodate strings of different sizes, from a single character to thousands of characters. This flexibility is crucial for handling a wide variety of data formats, such as names, addresses, or any form of textual data where the length cannot be predetermined.

The other statements presented do not accurately reflect the properties of string data types. While in some contexts strings might have fixed-length representations, this is not universally true of all string data types. Also, while strings can indeed include digits, they do not "contain digits but not numbers" as that distinction is not meaningful; a string can represent numeric values, but these are still stored as character sequences. String representation is primarily for characters; hence they are not exclusively designated for character usage only.