two date ranges for train data

[playgithub]

https://qlib.readthedocs.io/en/latest/component/workflow.html#complete-example

...
data_handler_config: &data_handler_config
    start_time: 2008-01-01
    end_time: 2020-08-01
    fit_start_time: 2008-01-01
    fit_end_time: 2014-12-31
    instruments: *market
...
task:
...
    dataset:
        class: DatasetH
        module_path: qlib.data.dataset
        kwargs:
            handler:
                class: Alpha158
                module_path: qlib.contrib.data.handler
                kwargs: *data_handler_config
            segments:
                train: [2008-01-01, 2014-12-31]
                valid: [2015-01-01, 2016-12-31]
                test: [2017-01-01, 2020-08-01]
...

Both task.dataset.kwargs.data_handler_config(fit_start_time/fit_end_time) and task.dataset.segments(train) have a date range for train data, confusing.