Mathematical operators in numeric input fields

Hi,

This is for the wishlist.

It would be nice to allow very simple operators in numeric input fields.

For exemple, for the X position of an object, setting it from:

                          500,000
to:
                        500,000+25

would automaticaly replace (when hit Enter) with:
                            525,000

It means that the equation is not keep in the SVG file or even in memory.

Operations would be:
+, -, *, / and %

The % is not for modulo but for percent:
                     500,000+50% => 750,000
                     500,000-10% => 450,000

Thanks!