A computer-based report is generated based on report data and according to a report definition describing how to render the report on a page or screen or the like. The report definition may have standard data recognizable to a report processor, and may also have custom data not recognizable to the report processor but to, for example, a rendering extension of such processor. The report processor though not recognizing the custom data. does not delete or ignore but instead passes the custom data in an intermediate format. Thus, the rendering extension which does recognize the passed-through custom data can in fact interpret and act upon such custom data.