Cross is usually used for looking up data from one project in another project, but it also works within a project to look up a value from one cell in a different column in the same project. So for example if we have "Project 1" with "Column A" and "Column B". We want to know if a value in a cell in Column A appears somewhere in Column B(not necessarily the same row, just anywhere in the Column). To achieve this you can add a "Custom text facet" in Column A with the expression:
value.cross("Project 1", "Column B").length()
This will give you a facet with the number of matches the value in Column A has in Column B. Those that give an error have no matches. You can further change the expression used if you want different information in the facet.
Hope this helps