Document default values on viewport and scissor rectangles.

src/Magnum/AbstractFramebuffer.h

@@ -276,7 +276,9 @@ class MAGNUM_EXPORT AbstractFramebuffer {
          *
          * Saves the viewport to be used at later time in @ref bind(). If the
          * framebuffer is currently bound, updates the viewport to given
-         * rectangle.
+         * rectangle. Initial value in @ref DefaultFramebuffer is set to cover
+         * whole window, in @ref Framebuffer the initial value is specified in
+         * constructor.
          * @see @ref maxViewportSize(), @fn_gl{Viewport}
          */
         AbstractFramebuffer& setViewport(const Range2Di& rectangle);

src/Magnum/DefaultFramebuffer.h

@@ -38,8 +38,7 @@ namespace Magnum {
 
 Default framebuffer, i.e. the actual screen surface. It is automatically
 created when @ref Context is created and it is available through global
-variable @ref defaultFramebuffer. It is by default mapped to whole screen
-surface.
+variable @ref defaultFramebuffer.
 
 @anchor DefaultFramebuffer-usage
 ## Usage

src/Magnum/Renderer.h

@@ -483,6 +483,7 @@ class MAGNUM_EXPORT Renderer {
         /**
          * @brief Set scissor rectangle
          *
+         * Initial value is set to cover whole window.
          * @see @ref Feature::ScissorTest, @fn_gl{Scissor}
          */
         static void setScissor(const Range2Di& rectangle);