getStringKeys() hasn't been GS2ified, doesn't work with Object references.
PHP Code:
function getArrayKeys(array, key) {
temp.e = 0; // The array element
temp.out = 0; // The output array
for (e: array) {
if (e.starts(key)) {
out.add(e.substring(key.length()));
}
}
return out;
}