The directive .set mips3d makes the assembler accept instructions from the MIPS-3D Application Specific Extension from that point on in the assembly. The .set nomips3d directive prevents MIPS-3D instructions from being accepted.
The directive .set mdmx makes the assembler accept instructions from the MDMX Application Specific Extension from that point on in the assembly. The .set nomdmx directive prevents MDMX instructions from being accepted.
Traditional mips assemblers do not support these directives.