PHP Notice: Only variables should be passed by reference in...

[ner00]

The array_pop() function's parameter is passed "by reference", meaning the function directly modifies the variable that is passed into the function https://github.com/stremlau/html5_notifier/blob/5d85947e16ea9cac4544c59666fe0ff13ba2a44a/html5_notifier.php#L59

Due to this behaviour, you can't pass a function directly into array_pop(), you have to store the output of explode() into a variable first, then pass that variable into array_pop().

source: https://stackoverflow.com/a/45109918/924855

Note: also replaced indentation tabs with spaces, it was a mix of both.