Determines whether the Input Method Editor (IME) composition window is active.
true if the IME window is open; otherwise, false.
When the input method editor is active, it contains the composition string which may or may not be inserted into the document. At this moment, the contents of the document is ambiguous and should not be taken as is. Use the IsImeWindowOpen property to determine whether the IME input is incomplete, to prevent text-related commands from executing.
The RichEditControl.CloseImeWindow method forces the input method editor to finalize the composition and send the resulting string to the document (or cancel the input).