docs: describe XIM text and placement as they now are

README.md

@@ -25,8 +25,9 @@ the results. `Esc` cancels composition.
 
 Hiragana mode composes a complete reading before offering Kanji candidates.
 Katakana mode does not perform Kanji conversion. Emoji and Hanja searches
-return to the previous mode after use. Hanja lookup currently supports one
+return to the previous mode after use; switching language during a search
-modern Hangul syllable at a time.
+commits the shown query. The Hanja dictionary lists one modern Hangul
+syllable at a time.
 
 ## Preedit and candidates
 
@@ -37,9 +38,10 @@ modern Hangul syllable at a time.
 | XIM PreeditPosition | strans popup | strans popup |
 | XIM PreeditNothing | strans popup | strans popup |
 
-XIM supports `UTF8_STRING` and `COMPOUND_TEXT`. Position clients place the
+XIM text travels as `COMPOUND_TEXT`, which carries any UTF-8. A client that
-popup from `XNSpotLocation`; otherwise XIM placement falls back to the bottom
+sends `XNSpotLocation` gets the popup at that spot whatever its preedit
-of the focus or client window.
+style; otherwise the popup sits under the focus window, or under the client
+window when no focus window is set.
 
 The popup is an X11 window, XIM is X11-only, and GTK popup placement converts
 the GTK caret to X11 root coordinates. There is no native Wayland popup
@@ -82,7 +84,7 @@ and cmp/diff, plus development files for:
 
 - Plan 9 port (`9c`, `9l`, `libthread`, and `libbio`);
 - D-Bus development files;
-- XCB, XCB RandR, xcb-imdkit, xkbcommon, and xkbcommon-x11;
+- XCB, XCB RandR, XCB XKB, xcb-imdkit, xkbcommon, and xkbcommon-x11;
 - Pango, PangoCairo, Cairo, and Fontconfig;
 - GTK 3, plus libibus and Xlib for the live clients;
 - Xvfb for the X11 live tests;