MAXScript Language Improvements in 3ds Max 5
TYPE_INDEX, TYPE_INDEX_TAB, TYPE_MATRIX3, and TYPE_MATRIX3_TAB have been added as supported PB2 data types in MAXScript. TYPE_INDEX is used for parameters that are 0-based, but are exposed in MAXScript as 1-based - for example, a vertex index.
The above data types are also available in scripted parameter blocks with types of #index, #indexTab, #matrix3, and #matrix3Tab, respectively.
type:#index is animatable,#matrix3 is not.
type:#index should behave in the same manner as type:#int, except the data value stored is 0-based but is seen by MAXScript as 1-based. So if you had an object using an animated height1 property (as defined above), you would see something like: