The following types of variables exist:
1) Logical - MS_TRUE
2) Map units - MS_FEET
3) Layer, Shape, & Shapefile types - MS_LAYER_POINT
4) Label attributes for Type, Position, & Size - MS_TRUETYPE
5) Query modes - MS_SINGLE
6) Connection types - MS_SHAPEFILE
7) Image types - MS_PNG
8) Line joins - MS_CJC_ROUND
9) Return codes - MS_SUCCESS