This example demonstrates fundamental SVG manipulation through a simple interactive circle. The page displays a single red circle created with the SVG `<circle>` element, which changes to green when a user clicks the "changecolor" button. The interaction relies on the HTML `onclick` attribute, which calls the `changecolor()` JavaScript function that toggles the circle’s fill style via the `document.getElementById` API. The rendering approach is purely declarative SVG with inline styling, and the code uses no external libraries.