Operations between values

The <b> element is used to execute operations between two values. The operation is defined by its id, for example:

<b id="+">
    <p id="10"></p>
    <p id="foo"></p>
</b>
<b id="*">
    <p id="10"></p>
    <p id="foo"></p>
</b>

is compiled as

10 + foo
10 * foo