how set different legend for different lines?

[ChenyangRan]

Hi, I try to plot different notations for lines. However, the Post Processor for Legends seems cannot work, when input

lambda legend: ('itr100','itr200','itr200')

The error is: The 'legendgroup' property is a string and must be specified as: - A string - A number that will be converted to a string

It means I can only set the same notations for lines?