DOT(.) after Ampersand (host variable)& considering as a part of variable name?

I know heading is not so clear.This is the picture

I am using &a开发者_StackOverflowmp;a it is considering it as $a. ,in the output &a and &a. is giving the same output. and why single .(DOT) after &a is giving no error but if we put any character, operator or wild characters after &a gives error.

This is the code.

BEGIN
  FOr i in &&a...3 LOOP
     DBMS_OUTPUT.PUT_LINE(i||' '||&a.||' '||&a);
END LOOP;
END;

Output Coming

1 1 1
2 1 1
3 1 1

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The dot is a delimiter for the & define. In most cases you won't notice a difference, but if you for some reason didn't have whitespace or similar after the variable name it could cause confusion. For example, if you were concatenating something with your variable in a string, '&asomething', it would ask for a variable named 'asomething'. If you did it as '&a.something' then it would ask for a variable named 'a' and tack 'something' on the end of whatever value is supplied. Any other character after the &a would be treated as either part of the variable name or would cause an error if it isn't valid as part of the name.