Two questions about the PSD file format specicaition

Question

I'm a programmer dealing with a project to parse PSD files. When reading the official file format specification, I found that some fields of the file are not clarified:
1. There is a rectangle structure containing 4 fields: top, left, buttom, right. I wanna know whether these 4 fields can be negative values and is there a rule that the buttom shoud be larger than the top and the right shoud be larger than the left
2. The PSD file contains a color mode section. But if the color mode is RGB, the color mode section contians no data but a 4-byte length field whose value is set to 0. This is true for files in RGB mode 8-bit channel. But after convert the files to RGB mode 32-bit channel using photoshop, the whole color mode section is no long exist.
These two questions may be somehow technical, I would be thankful if someone can give me a hand.

Answer 1

1) was covered in the documentation at one time.  Yes, many of them can be negative, that's why they're signed values.  Valid rectangles will have the bottom greater than the top, and the right greater than the left. But you can also have empty rectangles, and sometimes invalid rectangles (because the values don't matter).
2) Not sure what you're asking...  color mode is just a single enumeration for RGB, CMYK, etc.