> * Native support for arrays. I mentioned a few above. `<<Faults$$>>` and `<<$$>>` -- guess what these two mean if you see this first time? You would never guess. It's an empty array and an empty element, you've just failed.

<< means it relates to starting an array, $>> means it is the end, $$ meaning something else — an empty array!

The xᴍʟ alternative is a bodge:

    public class PurchaseOrder
    {
        public Item[] ItemsOrders;
    }

    public class Item
    {
        public string ItemID;
        public decimal ItemPrice;
    }

serializes to:

    <PurchaseOrder>
        <ItemsOrders>
            <Item>
                <ItemID>aaa111</ItemID>
                <ItemPrice>34.22</ItemPrice>
            </Item>
            <Item>
                <ItemID>bbb222</ItemID>
                <ItemPrice>2.89</ItemPrice>
            </Item> 
        </ItemsOrders>
    </PurchaseOrder>

Where the array is marked up as two sub elements both called <Item>:

Xᴇɴᴏɴ has first class support for arrays:

  <PurchaseOrder>
      <<ItemsOrders>
          <ItemID=aaa111>
          <ItemPrice=34.22>
      <&>
          <ItemID=bbb222>
          <ItemPrice=2.89>
      <$>>
  <$>

The elements may be scalars so

  <PurchaseOrder>
      <<ItemsOrders>
      <$>>
  <$>

has an array with one item of the empty string. So a separate syntax for empty arrays is required!

  <PurchaseOrder>
      <<ItemsOrders$$>>
  <$>