An animation can be selected. Pieces of the documents that pertain to the selected animation can be extracted from the document closure for the web page in which the animation appears. A composite data structure can be created therefrom. The winning set of @keyframes rules referenced by the animation-name property of a style rule (the virtual winning rule) can be computed and represented in a data structure. The winning animation properties can establish the timing properties to preview and edit the animation in a user interface without running the whole application. The data structure represented in the visual preview can be edited by applying user gestures to the animation displayed in a preview user interface (UI). The user changes can be mapped to changes to property values in the data structure and the underlying documents.