11. A computer program product comprising a non-transitory computer readable storage medium having program code embodied therewith, the program code executable by at least one processor to: render, by an application executing on a target platform, a document that specifies one or more widgets of each of a first widget type and a second widget type, the rendering including: in response to determining, by the application, that the application includes a first native widget renderer for rendering the one or more widgets of the first widget type, wherein the first native widget renderer is written using an application program interface (API) that is native to the target platform, render the one or more widgets of the first widget type by the first native widget renderer for the first widget type, and in response to determining, by the application, that the application does not include a second native widget renderer for rendering the one or more widgets of the second widget type, wherein the second native widget renderer is written using the API that is native to the target platform, render the one or more widgets of the second widget type, by a default widget renderer for rendering the second widget type, wherein the default widget renderer is written using cross-platform code for a plurality of target platforms including the target platform.
11. A computer program product comprising a non-transitory computer readable storage medium having program code embodied therewith, the program code executable by at least one processor to: render, by an application executing on a target platform, a document that specifies one or more widgets of each of a first widget type and a second widget type, the rendering including: in response to determining, by the application, that the application includes a first native widget renderer for rendering the one or more widgets of the first widget type, wherein the first native widget renderer is written using an application program interface (API) that is native to the target platform, render the one or more widgets of the first widget type by the first native widget renderer for the first widget type, and in response to determining, by the application, that the application does not include a second native widget renderer for rendering the one or more widgets of the second widget type, wherein the second native widget renderer is written using the API that is native to the target platform, render the one or more widgets of the second widget type, by a default widget renderer for rendering the second widget type, wherein the default widget renderer is written using cross-platform code for a plurality of target platforms including the target platform. 15. The computer program product of claim 11 , further comprising: render, by the application executing on the target platform, one or more static elements specified by the document.