Basic information on testRunner

Hello,

I have gone through basics of groovy scripting in SOAPUI. I want to know whether testRunner is a variable or an interface?

If it is an interface according to this link: http://www.soapui.org/apidocs/com/eviware/soapui/model/testsuite/TestRunner.html

then how are we able to use the dot operator after writing testRunner?

[Sample code]

log.info testRunner.testCase.testSuite.project.name
log.info testRunner.testCase.testSuite.getLabel()
log.info testRunner.testCase.getLabel()

[/Sample code]