Cursors order in query using composite index

I wonder how records are arranged in queries that use composite indices.

Let's consider this example.

let objetStore = db.createObjectStore('article',{keyPath : 'id'});
objectStore.createIndex('userid-date',['userid','date_created']);

db.transaction('article').objectStore('article').index('userid-date').openCursor(IDBKeyRange.bound([1,new Date(new Date() - 365*86400*1000)],[100,new Date()])).onsuccess = function(e){

};

Are the records in the above query ordered by userid or date_created? Why?