How to reproduce:
1. Open the attached project "UndocumentedFlatBarrier"
2. Go to Repro -> Run Bug 07
3. Observe the two identical parent/child/grandchild stacks in the Game view, which differ only in the child declaring "none" versus "0deg 0deg"
4. Open the -unity-curvature entry in the USS supported-properties documentation and the Curvature struct scripting reference, and read the description of the property and its accepted values "none | <angle>{1,2}"
5. Observe the results
Expected results: The documentation states that "0deg" and "none" are not equivalent, and that declaring "0deg" on a descendant of a curved element makes that descendant and its subtree render flat
Actual results: Neither the USS property table, the Curvature scripting reference, nor the UI Builder and VisualElement inspector tooltips mention the difference, so "0deg" reads as a no-op
Reproducible with: 6000.7.0a6
Can't test with: 6000.3.17f1, 6000.5.10f1, 6000.6.0f1, 6000.7.0a5 (No such property)
Reproducible on: Ubuntu 24.04.4 LTS (Intel i9-10980XE), macOS Tahoe 26 (M1)
Not reproducible on: No other environment tested
Note: The behaviour itself is intentional (the code comments call it an
"explicit-0deg flat barrier"), so this is a documentation gap rather than a
behaviour bug.