From Valve Developer Community
- Minimum DX Level (mindxlevel)
- Maximum DX Level (maxdxlevel)
- The entity will not exist if the engine is running outside the given range of DirectX Versions. Only used by Orange Box and 2013 SDK games.
- Warning: If these are used, the object may break when the user switches their DirectX settings.
- Default (no bounding)
- DX9 SM2
- DX9 SM3