When a diagram is saved, CaseTalk can write an accompanying .igdx file - an XML rendering of the same picture, meant for exchange with other tools and for reading a diagram without the binary file.

Anything that was grouped on the diagram was missing from that XML. The elements were written, but the fact that some of them belong together in a group - and the way that group looks (its title, fill colour, border colour, border width and border style) - was not, so a diagram read back from .igdx showed no groups at all.

The .igdx file now records, for every element, which group it belongs to, plus a separate section holding the appearance of each group. The outline drawn around a group is not stored: it is calculated from the members, exactly as on screen, so a group keeps hugging its elements wherever they are moved.

Older .igdx files without groups still read normally, and the new files can still be read by anything that only knows the previous format.