How hard is it to know basic XML?! My goodness, this is a 30 second thing to learn.
Make the first line in your file this:
<?xml version="1.0" ?>
or this:
<?xml version="1.0" encoding="us-ascii" ?>
Substitute whatever encoding you want there, or leave it out to assume an encoding of utf-8.
Now, construct your file in a heirarchial format, just like HTML is. You can only have one root node though, but any node can have any number of subnodes and any number of arguments, although arguments need to have double quotes around the values. Standard C type naming rules apply, and names are case-sensitive. Two or more nodes of the same name can exist at the same level under the same node and are treated as distinct (the data is not joined in parsers.)
Here's a small example:
<?xml version="1.0" encoding="utf-8" ?>
<rootnode arg1="value1" arg2="value2">
<subnode>
<interiornode>This is text</interiornode>
</subnode>
<subnode>
<node_with_no_value />
<node_with_value>Hello World</node_with_value>
</subnode>
<newnode argument="value">
<subnode>
<text>Hiya</text>
</subnode>
</newnode>
</rootnode>