I really don't know how to describe this in a way that makes sense. The following is the best I could come up with.
Note: 1-16chrd.dat is a special case that is used on the inside of a curved primitive where it joins geometry that cannot make use of a curved primitive. The primitive file itself is simply a reference to empty.dat, which under normal circumstances does not draw anything. However, in tools that support primitive substitution, the curved primitive it is attached to would normally in this case create a gap when rendered using more than 16 points to form a circle. In that case, the substituted version of this normally empty primitive would fill in the gap between the curve and the other geometry.
Note: 1-16chrd.dat is a special case that is used on the inside of a curved primitive where it joins geometry that cannot make use of a curved primitive. The primitive file itself is simply a reference to empty.dat, which under normal circumstances does not draw anything. However, in tools that support primitive substitution, the curved primitive it is attached to would normally in this case create a gap when rendered using more than 16 points to form a circle. In that case, the substituted version of this normally empty primitive would fill in the gap between the curve and the other geometry.