LilyPond Contributor's Guide: 10.13.6 Debugging tips

### 10.13.6 Debugging tips

A few questions to ask yourself when working with pure properties:

- Is the property really pure? Are you sure that its value could not be changed later in the compiling process due to other changes?
- Can the property be made to correspond even more exactly with the eventual impure property?
- For a spanner, is the pure property changing correctly depending on the starting and ending points of the spanner?
- For an Item, will the item’s pure height need to act in horizontal spacing but not in vertical spacing? If so, use extra-spacing-height instead of pure height.

#### LilyPond — Contributor’s Guide v2.24.4 (stable-branch).