1. A method comprising: receiving, by a run-time edit engine executed by a processor, source code of a web page that includes code defining run-time editing capabilities for editing a first region of an output presentation of the web page and a second region of the output presentation of the web page; during run-time, receiving, by the run-time edit engine, a first request to edit the first region and a second request to edit the second region; determining, by the run-time edit engine, that a client from which the first and second requests are received is authorized to perform a first plurality of run-time editing capabilities in the first region and a second plurality of run-time editing capabilities in the second region, wherein the second plurality of run-time editing capabilities includes at least one run-time editing capability that is not included in the first plurality of run-time editing capabilities that the client is authorized to perform for the first region, wherein the first and second pluralities of run-time editing capabilities are determined based on the code defining the run-time editing capabilities; and responding to the first and second requests by interpreting, by the run-time edit engine, the code defining the run-time editing capabilities during run-time of the web page to enable the first and second pluralities of run-time editing capabilities that the client is authorized to perform in the respective first and second regions.
4. The method of claim 1 further comprising: responsive to the first and second requests for run-time editing of the web page, downloading code to a client computer that is executable by the client computer to present an editing interface that provides tools for performing the run-time editing according to the defined run-time editing capabilities.