Specifies the Url that will be opened on OnClick action.
Url property can open not only the browser window but also a default email client and some other files. For example:
url http://enigmaprotector.com/ opens a browser window with the current address,
url mailto:firstname.lastname@example.org opens a default email client with the offer to create email for email@example.com
url License.txt opens a Windows notepad with the License.txt file.