11.55 spline

spline [ <range> ] <function name>()
       ( <filename> | { <expression> } | { <vector obj> } )
       [ every { <expression> } ]
       [ index <value> ]
       [ select <expression> ]
       [ using { <expression> } ]

The spline command is an alias for the interpolate spline command. See the entry for the interpolate command for more details.