How to check annotations in a custom dataset

[kupferb]

In the customizing datasets tutorial in the "Check the annotations of the customized dataset" part its written that:

The classes fields in your config file should have exactly the same elements and the same order with the A[8] in txt annotations. MMRotate automatically maps the uncontinuous id in categories to the continuous label indices, so the string order of name in categories field affects the order of label indices. Meanwhile, the string order of classes in config affects the label text during visualization of predicted bounding boxes.

1. What is the meaning of "The classes fields in your config file should have exactly the same elements and the same order with the A[8] in txt annotations"? that if my classes are classes=('a','b','c') then in every annotation file (e.g., annot_1.txt) the order of the annotations class a should be before b and b should be before c? if so then in the DOTA_1 dataset original annotations txt files there are lots of files that doesn't obey this rule (e.g., some annotations files contains ship before harbor while other annotations files contains harbor before ship)
2. In which file/s exactly can I find id, categories and name?