website: cbt

website/app/vt/cbt/page.mdx

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+import VTSequence from "@/components/VTSequence";
+
+# Cursor Backward Tabulation (CBT)
+
+<VTSequence sequence={["CSI", "Pn", "Z"]} />
+
+Move the cursor `n` tabs left.
+
+The leftmost valid column for this operation is the first column. If
+[origin mode](#TODO) is enabled, then the leftmost valid column for this
+operatin is the [left margin](#TODO).
+
+Move the cursor left until the cursor position is on a tabstop. If the
+cursor would move past the leftmost valid column, the cursor remains at
+the leftmost valid column and the operation completes. Repeat this process
+`n` times.
+
+Tabstops are dynamic and can be set with escape sequences such as
+[horizontal tab set (HTS)](/vt/hts), [tab clear (TBC)](/vt/tbc), etc.
+A terminal emulator may default tabstops at any interval, though an interval
+of 8 spaces is most common.
+
+## Validation
+
+### CBT V-1: Left Beyond First Column
+
+```bash
+printf "\033[?W" # reset tab stops
+printf "\033[10Z"
+printf "A"
+```
+
+```
+|Ac________|
+```
+
+### CBT V-2: Left Beyond First Column
+
+```bash
+printf "\033[?W" # reset tab stops
+printf "\033[1;10"
+printf "X"
+printf "\033[Z"
+printf "A"
+```
+
+```
+|________AX|
+```
+
+### CBT V-3: Left Starting on Tabstop
+
+```bash
+printf "\033[?W" # reset tab stops
+printf "\033[1;9H"
+printf "X"
+printf "\033[1;9H"
+printf "\033[Z"
+printf "A"
+```
+
+```
+|A_______X_|
+```
+
+### CBT V-4: Left Margin with Origin Mode
+
+```bash
+printf "\033[1;1H" # move to top-left
+printf "\033[0J" # clear screen
+printf "\033[?W" # reset tab stops
+printf "\033[?6h" # enable origin mode
+printf "\033[?69h" # enable left/right margins
+printf "\033[3;6s" # scroll region left/right
+printf "\033[1;2H" # move cursor in region
+printf "X"
+printf "\033[Z"
+printf "A"
+```
+
+```
+|__AX______|
+```