This blend transition filter is used to control the fading in and out of the filtered element. This would be used to create a dissolve effect.
The duration name=value pair specifies a floating point value in seconds which controls how quickly the effect should take place.
The use of this feature is deprecated in favor of the named transitions introduced in later versions of MSIE and which can be used as static or transitional effects.
Filters are defined in style sheets as if they were a function call with its arguments expressed as name=value pairs. This is not the typical way to define arguments so you should be aware of this anomaly when working with filters.