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: