Accurate diffs you can apply
The line diff uses the Myers algorithm and the exported .patch is a standard unified diff, including “No newline at end of file” markers. The test suite applies generated patches with GNU patch to make sure they reproduce the changed file exactly.
Also inside the editor
In the full editor, Local history can compare any snapshot with the current file, and “Compare with another file” diffs two project files. You can pull individual changes back from an older snapshot without restoring everything.
Questions
Is there a size limit?
Diffs of several thousand lines are fine. Very different large files fall back to a full replace view rather than freezing.
Does it ignore whitespace?
Not currently; whitespace changes are shown. Format both sides first if you only care about structure.
Can I edit both sides?
Yes. Both panes are editable in side-by-side mode.