SCS_CHANGECLAUSE effects the string and attribute for both the composition string and the reading of the composition string.
If it is necessary, IME may update the candidate information and generate the candidate messages IMN_OPENCANDIDATE, IMN_CHANGECANDIDATE, or IMN_CLOSECANDIDATE.
IME can not finalize the composition string.
If the lpRead parameter of ImeSetCompositionString is available, the IME follows the new reading clause information of lpRead. The IME must correct the attribute of the reading of the composition string. The IME may then update the composition string, the attribute, and the clause information of the composition string. The IME generates WM_IME_COMPOSITION with (GCS_COMP | GCS_COMPREAD).
If the lpComp parameter of ImeSetCompositionString is available, the IME follows the new clause information. The IME must correct the composition string and the attribute of the composition string. The IME may then update the reading attribute and the clause information of reading. The IME generates WM_IME_COMPOSITION with (GCS_COMPSTR | GCS_COMPREAD).
If both lpRead and lpComp are available, and if the IME can accept the new information, the IME sets the new information into the COMPOSITION structure of hIMC and generates WM_IME_COMPOSITION with (GCS_COMP | GCS_COMPREAD).