TM4C123 GPIO_DATA Question
If you read the section you quoted. You’ll see that bits [9:2] of the address are used as a mask to allow changing only some of the bits on a write. Those bits correspond to a hex value of 3FC. Therefore, they are enabling writes to all 8 bits. 

If they wanted to make sure that only the bit corresponding to the LED were changed, the 3FC would be changed to the bit position, shifted left 2 bits.

This is actually a very nice feature as it allows separate execution threads to interact with different bits without having to go use read-modify-write which could clobber the same in another thread.