1. DomName('WebGL2RenderingContext.copyTexSubImage2D')
  2. DocsEditable()
  3. Experimental()
void copyTexSubImage2D(int target, int level, int xoffset, int yoffset, int x, int y, int width, int height)

Source 

@DomName('WebGL2RenderingContext.copyTexSubImage2D')
@DocsEditable()
@Experimental() // untriaged
void copyTexSubImage2D(int target, int level, int xoffset, int yoffset, int x, int y, int width, int height) => _blink.BlinkWebGL2RenderingContext.instance.copyTexSubImage2D_Callback_8_(this, target, level, xoffset, yoffset, x, y, width, height);