It acts similiarly to Excel's MID function. Function is for string extraction. You select the starting number and the amount of characters you want to extract.
Usage
MID(text, start_num, num_chars)
Arguments
text
From whch text should it return the string?
start_num
Where should it start counting from?
num_chars
How many characters should it return?
Value
In this example we want to extract "kata" from this string. So we specify 5 as the starting number and 4 as the amount of characters to extract. Function will always return character class.