What's the meaning of the GeosetAnim section of MDL file?

What is the meaning of the GeosetAnim section of MDL?

For example:
GeosetAnim {
Alpha 3 {
DontInterp,
67: 0,
65033: 0,
240000: 0,
}
GeosetId 0,
}

What's the meaning of "67: 0, 5033: 0, 240000: 0"?

These control the visibilty of geosets (the actual models), in cases where a given part of a model isn't always visible. An example of this would be the gold sac on the peasant. It is invisible during non "gold" animations. The syntax is like this:
keyframe : alpha

Keyframes refer to animation (look at the very top of the mdl file to see all of the animations defined by keyframe). Alpha refers to how visible a geoset is. Setting this to zero makes the geoset invisible. All units with a "guts" (corpse) geoset have it set to zero during all non-decay animations, for example.

1. Is the Warcraft3's animation driven by keyframe system or skeleton system?
2. If it is keyframe system, what's the use of bone section?

3. For Example:
//NerubianZiggurat.mdl has only two geosets, two GeosetAnim of course.

Anim "Stand" { //only show GeosetId 1.
Interval { 67, 333 },
MinimumExtent { -144.325, -133.077, -79.241 },
MaximumExtent { 116.375, 127.202, 110.869 },
BoundsRadius 162.519,
}
Anim "Portrait -1" { //show all.
Interval { 667, 1067 },
MinimumExtent { -199.141, -312.315, -145.525 },
MaximumExtent { 116.375, 264.481, 373.591 },
BoundsRadius 418.845,
}
Anim "Death" {
Interval { 65033, 67300 },
NonLooping,
MinimumExtent { -144.325, -133.077, -79.241 },
MaximumExtent { 116.375, 127.202, 110.869 },
BoundsRadius 162.519,
}
Anim "Decay" { //show nothing
Interval { 240000, 300000 },
MinimumExtent { 3.40282e+038, 3.40282e+038, 3.40282e+038 },
MaximumExtent { -3.40282e+038, -3.40282e+038, -3.40282e+038 },
}

GeosetAnim {
Alpha 3 {
DontInterp,
67: 0, emote_confused //Frame 67 is not shown, but how to do with Stand's end frame 333 ?
65033: 0,
240000: 0,
}
GeosetId 0,
}
GeosetAnim {
Alpha 3 {
DontInterp,
65033: 1,
65467: 0,
240000: 0,
}
GeosetId 1,
} emote_confused //can't find Portrait's Frame { 667, 1067 }, what does it mean?


Are there any documents about the meanings of the mdl sections?
I have just been troubled by these questions for quite a while.

Thanks ahead for your reply!