Data in the assembly cannot start with a letter! 0 before the beginning of a letter

If the data in the source code starts with a letter , The compiler will report an error

For example, the following code , compiling

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        assume cs:code
        
code segment
        
start:
        
  mov ax,ffffH
        
code ends
        
end start
       
       

        
1.
        
2.
        
3.
        
4.
        
5.
        
6.
       

The following errors will be reported when compiling ： 

So it will ffffh Add a zero before it , become 0ffffh

Then the compiler will not report an error