How to reproduce:
1. Create a new Unity project
2. Go to Project Settings -> UI Toolkit and enable "Enable Grid Layout"
3. In the Project window, right-click -> Create -> UI Toolkit -> Style Sheet (USS)
4. Open the created USS file and add the following rules:
#a { grid-column: 2 / 4; }
#b { grid-row: 1 / 3; }
#c { grid-column: 2 / span 2; }
#d { grid-column: span 2; }
#e { grid-column-start: 2; grid-column-end: 4; }
5. Save the file
6. Observe the Console
Expected results: All five rules import without warnings, since "<integer> / <integer>" and "<integer> / span <integer>" both match the grammar quoted in the warning
Actual results: The three rules using the "/" separator each throw "warning: Expected (<integer> [ / [ <integer> | span <integer> ] ]? | span <integer>) but found '2/4'", while "span 2" and the longhand form import cleanly
Reproducible with: 6000.7.0a5
Not reproducible with: 6000.0.81f1, 6000.5.9f1, 6000.6.0b9, 6000.7.0a4
Reproducible on: macOS Tahoe 26.6 (M1 Max)
Not reproducible on: No other environment tested