How to pass value in 'tag' command in liquibase.gradle plugin?

I’m studying liquibase.gradle plugin and i realy want to understand how to uses it.
Please, tell me how to use ‘tag’ command? In documentation i read that it must me write like a simple gradle task. That all. There is example of build in but in file nothing about ‘tag’ task settings. No examples there. And i can’t find something in google about that.
Error in comand line said that “The Liquibase ‘tag’ command requires a value”
What does it mean and how i can set in there in Liquibase gradle plugin?
Thanks for your answers.