For the attribute kernelUnitLength = "< number optional-number >", the first number is the dx value. The second number is the dy value. If the dy value is not specified, it defaults to the same value as dx.
kernelUnitLength indicates the intended distance in current filter units (as determined by the value of the primitiveUnits attribute) for dx and dy, respectively, in the surface normal calculation formulas. By specifying value(s) for kernelUnitLength, the kernel becomes defined in a scalable, abstract coordinate system. If kernelUnitLength is not specified, the dx and dy values should represent very small deltas relative to a given (x, y) position.
For some level of consistency across display media and browsers, it is necessary that a value be provided for at least one of filterRes and kernelUnitLength.
- Scalable Vector Graphics: Filter Effects, Section 15.25.12
Microsoft Developer Network: [Windows Internet Explorer API reference Article]