The TS_OFFSCREEN_CAPABILITYSET structure is used to advertise support for off-screen bitmap caching (see [MS-RDPEGDI] section 3.1.1.1.5). This capability is only sent from client to server.
file:///C:/ts_dev/TestSuites/MS-RDPBCGR/TestSuite/Src/TD/latest_XMLS_16may/RDPBCGR/ _rfc_ms-rdpbcgr2_1_6_1_10.xml
 /// <summary>
 /// 2.2.7.1.9 
 /// Check the requirements in structure TS_OFFSCREEN_CAPABILITYSET
 /// </summary>
 /// <param name="offscreen"></param>
 public void VerifyStructure(TS_OFFSCREEN_CAPABILITYSET offscreen)
 {
     bool isSatisfied = offscreen.offscreenSupportLevel == offscreenSupportLevel_Values.TRUE ||
         offscreen.offscreenSupportLevel == offscreenSupportLevel_Values.FALSE;
     Site.Assert.IsTrue(isSatisfied, "offscreenSupportLevel field of TS_OFFSCREEN_CAPABILITYSET must be FALSE (0x00000000) or TRUE (0x00000001).");
 }