This is taken from this question (with permission ofcourse). I'll quote:
Create a function which takes a string, and it should return true or false based on whether the input consists of only a repeated character sequence. The length of given string is always greater than 1 and the character sequence must have at least one repetition.
'aa' //true 'aaa' //true 'abcabcabc' //true 'aba' //false 'ababa' //false 'weqweqweqweqweqw' // false
Specifically, the check for a string strictly composed of repeating substrings (Update) can output any true or false representation, but no error output please. Strictly alphhanumeric strings. Otherwise standard code golf rules. Shortest answer in bytes for each language wins.