Pascal, contrary to what the article states, allows any subrange of integer as an array index. For example,

    kernel: array[-3..3,-3..3] of real;

is a 7x7 array. It has negative indices, e.g.

   x := kernel[-3,-3];

See https://www.tutorialspoint.com/pascal/pascal_arrays.htm

Sometimes you want negative indices, e.g. when performing a convolution on an image with a kernel.