Returns the composed XML string.

Adds an XML attribute name with value in the node.

Example:
| `Start XML Node`    | book |
| `Add XML Attribute` | id | bk101 |
| `Set XML Text`      | Meet Joe Black |
| `End XML Node`      |
| ${xmlString}        | Create XML String |
| `Should Be Equal As Strings` | ${xmlString} | <book id="bk101">Meet Joe Black</book> |

Result:
| true