These features are experimental, officially unsupported, and thus undocumented. If you want to explore, noting in advance that there are known bugs in this functionality:
repeataccepts an array, and you can refer to a given member of that array (i.e. within other expressions, e.g. to make the position a function of the data in the array) using
ifaccepts a boolean value, which will toggle whether the element is rendered on the stage.