what's the meaning of plain text file's executable attribute

Q1:
a plain text file name aa.txt
/home/apple/study/note $ ls -l aa.txt
-rwxrwxrwx 1 apple apple 42 Feb 28 20:02 aa.txt
My question is what's the meaningof a plain 's executable attribute
,it is "x" bit.

as I know,a plain text file can't be executed. only the executable file
,such as /usr/bin/xpdf should have the attribute of 'x'. so there is no
meaning for the plain text file to have the 'x' attribute,is it right?

Q2:
what's the difference between interrupt and trap.
what I know is that interrupt include software interrupt and hardware
interrupt.
handware interrupt : I/O ,NMI...
software interrupt : divisor is zero...
divisor is zero is a trap.
but,what's more about the difference?

thanks very much .
davinci

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