Technically, any COM component that implements IInputMethod can be selected into the input panel. The IsSIPInputMethod subkey is a shortcut that presents a list of IMs to a user without loading and querying each object for the IInputMethod interface.
IMs are installed in the system as in-process COM servers by using standard COM registry keys. The HKEY_CLAS_ROOT\CLSID key contains subkeys representing COM components. The subkeys are textual representations of class identifiers (CLSID). The CLSID subkeys contain an InprocServer32 subkey with a default value. This value specifies the DLL path that implements the component. The CLSID subkeys also contain a IsSIPInputMethod subkey with a default value equal to the "1" string. The following table shows examples of IM registry values.
Key |
Default value |
HKEY_CURRENT_USER\ CLSID\ {4a4a96d7-ae04-11d0-a4f8-00aa00a749b9} |
"MS QWERTY IM" |
HKEY_CURRENT_USER\ CLSID\ {4a4a96d7-ae04-11d0-a4f8-00aa00a749b9}\ InprocServer32 |
"\Windows\alphanum.dll" |
HKEY_CURRENT_USER\ CLSID\ {4a4a96d7-ae04-11d0-a4f8-00aa00a749b9}\ IsSIPInputMethod |
"1" |