1. canvasgradient api: addcolorstop

2. css property: stop-color

3. types: `calc()`: gradient color stops support

4. types: `<image>`: `<gradient>`: `conic-gradient()`: double-position color stops

5. types: `<image>`: `<gradient>`: `linear-gradient()`: double-position color stops

6. types: `<image>`: `<gradient>`: `radial-gradient()`: double-position color stops

7. types: `<image>`: `<gradient>`: `repeating-linear-gradient()`: double-position color stops

8. types: `<image>`: `<gradient>`: `repeating-radial-gradient()`: double-position color stops

9. svg element: stop: stop-color