A doubt in Assembly lang. Program (PIC16f877a)

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A program to clear Ram locations 20H-2FH using indirect addressing:
(from PIC16f87x datasheet, page 27)

movlw 20h
movwf fsr
next: clrf indf
incf fsr, f
btfss fsr, 4
goto next
end

i am not understanding the 5th line of this program..
Why are we checking for 4th bit of 2fH
"Literary education is of no value, if it is not able to build up a sound character"

    A doubt in Assembly lang. Program (PIC16f877a)