Boolean is a primitive data type and can take true or false state. XML-RPC boolean is same as the PHP boolean. In XML-RPC, booleans can only be represented with 1 or 0 unlike PHP where boolean can be represented by the keywords TRUE or FALSE, or a numerical 1 for true and 0 for false.

Example Declaration:

<param>
<value><boolean>1</boolean></value>
</param>