Here is a demonstration video that goes through this process (Add remove columns.mov, right click this link to save the movie to disk for better viewing):
Here is a DeviceEditor .xml saved design file resulting from saving after the demonstration above (Add remove columns.xml, right click and save link as to save the design file to disk):
The relative (combinatorial) arrangement of the parts in the collection defines the DNA sequence(s) to be constructed. The collection contains one or more columns, where the total number of columns is equal to the total number of parts desired to be assembled together into the resulting construct. Parts placed into adjacent columns will be adjacent in the resulting assembled DNA sequence(s) (with the last column cyclically followed by the first column for circular DNA designs such as plasmids). Parts in the same column are considered combinatorial variants of/alternatives for each other. That is to say, each individual construct in the resulting combinatorial library contains exactly one of the parts in each column.
Within the "Collection Info" tab in the panel on the right side of the DeviceEditor display, it is possible to append or insert a column in to the collection. If you would like to append a column to the collection, simply click the "Add Column" button. Otherwise (to insert a column), in the collection table, click on the column entry (highlighting it) that should follow the column you will be inserting; then, click the "Add Column" button.
Within the "Collection Info" tab in the panel on the right side of the DeviceEditor display, it is possible to remove a column from the collection. If you would like to remove the last column from the collection, simply click the "Remove Column" button. Otherwise (to remove another column from the collection), click on the column entry in the collection table (highlighting it) that you would like to remove; then, click the "Remove Column" button. Note that if you remove a column that contains parts, the parts will moved to the "holding pen" at the bottom of the design canvas.