When I try to mark with <input type = image>, but $ foo

When a form is sent, it may use image as the submit button, as shown below:
<Input SRC = "image.gif" NAME = "foo"> when you press any point in the image, two additional variables foo. x and foo. y are returned to the server with the form.
Because foo. x and foo. y are problematic names in PHP, they are automatically converted to variables $ foo_x and $ foo_y. It is converted during PHP processing.