website: ich split multi-cell

src/terminal/Terminal.zig

@@ -1620,7 +1620,9 @@ pub fn insertBlanks(self: *Terminal, count: usize) void {
         while (i < copyable) : (i += 1) {
             const to = right_limit - 1 - i;
             const from = copyable_end - i;
-            row.getCellPtr(to).* = row.getCell(from);
+            const src = row.getCell(from);
+            const dst = row.getCellPtr(to);
+            dst.* = src;
         }
     }
 

website/app/vt/ich/page.mdx

@@ -19,6 +19,11 @@ still reset.
 Existing cells shifted beyond the right margin are deleted. Inserted cells
 are blank with the background color colored according to the current SGR state.
 
+If a multi-cell character (such as "橋") is shifted so that the cell is split
+in half, the multi-cell character can either be clipped or erased. Typical
+behavior is to clip at the right edge of the screen and erase at a right
+margin, but either behavior is acceptable.
+
 ## Validation
 
 ### ICH V-1: No Scroll Region, Fits on Screen
@@ -101,3 +106,23 @@ printf "X"
 ```
 |XcABC_____|
 ```
+
+### ICH V-6: Split Wide Character
+
+```bash
+cols=$(tput cols)
+printf "\033[${cols}G"
+printf "\033[1D"
+printf "橋"
+printf "\033[2D"
+printf "\033[@"
+printf "X"
+```
+
+```
+|_______Xc_|
+```
+
+In this case, it is valid for the last cell to be blank or to clip the
+multi-cell character. xterm clips the character but many other terminals
+erase the cell.