keme wrote:"... not a simple [pattern]" suggests that adjusting the grid is also not an option.
That's exactly the reason why I wrote this. I already considered it, but I wasn't quite happy with changing a global setting for that. I really had hoped there would be an easier solution. It might still be possible with using the grid though, I'd just need to change it several times.
Did you know: You can drag snap lines out from the rulers.
I knew, but I honestly didn't even consider it. You're right though, it actually is faster indeed, I never would have guessed

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If you explain the desired snap pattern in more detail than "not simple", someone here may have suggestions for other workarounds.
The vertical lines are still fairly simple: I need one every 1.7 cm, but with a shift of 1 cm. I could use the margin to get the shift, then it would easily work with the grid. The interval changes somewhere in the middle of the page, since I have some wider shapes there, but I guess I could manually place snap lines there. After that, the pattern continues, just with a different shift.
For the horizontal lines I have alternating intervals, I haven't determined the precise values yet. The whole thing is a fairly large dependency tree, one of the lines is for the items, the other is for the labels in between, so I don't necessarily need both at the same time. That would reduce it to a single interval and I could use the grid again. Guess I'll try that then.