I'm trying learn TICKscript, but official documentation is messy.

I understand part about variable declaration and expressions in it. But then there are 'nodes'. What's they are?

UPD: I even found their EBNF: <https://docs.influxdata.com/kapacitor/v1.5/reference/spec/>, and there is no node definition in it.

What is a node in TICKscript?