From 4bbe449263a5411f1d55b4c08bfe535604e6a0d9 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Fri, 6 Oct 2023 12:47:45 -0700
Subject: [PATCH] website: cud

---
 website/app/vt/cud/page.mdx       | 76 +++++++++++++++++++++++++++++++
 website/components/VTSequence.tsx |  1 +
 2 files changed, 77 insertions(+)
 create mode 100644 website/app/vt/cud/page.mdx

diff --git a/website/app/vt/cud/page.mdx b/website/app/vt/cud/page.mdx
new file mode 100644
index 000000000..10ad7d493
--- /dev/null
+++ b/website/app/vt/cud/page.mdx
@@ -0,0 +1,76 @@
+import VTSequence from "@/components/VTSequence";
+
+# Cursor Down (CUD)
+
+<VTSequence sequence={["CSI", "Pn", "B"]} />
+
+Move the cursor `n` cells down.
+
+The parameter `n` must be an integer greater than or equal to 1. If `n` is less than
+or equal to 0, adjust `n` to be 1. If `n` is omitted, `n` defaults to 1.
+
+This sequence always unsets the pending wrap state.
+
+If the current cursor position is at or above the [bottom margin](#TODO),
+the lowest point the cursor can move is the bottom margin. If the current
+cursor position is below the bottom margin, the lowest point the cursor
+can move is the final row.
+
+This sequence never triggers scrolling.
+
+## Validation
+
+### CUD V-1: Cursor Down
+
+```bash
+printf "A"
+printf "\033[2B" # cursor down
+printf "X"
+```
+
+```
+|A_________|
+|__________|
+|_Xc_______|
+```
+
+### CUD V-2: Cursor Down Above Bottom Margin
+
+```bash
+printf "\033[1;1H" # move to top-left
+printf "\033[0J" # clear screen
+printf "\n\n\n\n" # screen is 4 high
+printf "\033[1;3r" # set scrolling region
+printf "A"
+printf "\033[5B" # cursor down
+printf "X"
+```
+
+```
+|A_________|
+|__________|
+|_Xc_______|
+|__________|
+```
+
+### CUD V-3: Cursor Down Below Bottom Margin
+
+```bash
+printf "\033[1;1H" # move to top-left
+printf "\033[0J" # clear screen
+printf "\n\n\n\n\n" # screen is 5 high
+printf "\033[1;3r" # set scrolling region
+printf "A"
+printf "\033[4;1H" # move below region
+printf "\033[5B" # cursor down
+printf "X"
+```
+
+```
+|A_________|
+|__________|
+|__________|
+|__________|
+|_Xc_______|
+```
+
diff --git a/website/components/VTSequence.tsx b/website/components/VTSequence.tsx
index 7cb2c0559..471719562 100644
--- a/website/components/VTSequence.tsx
+++ b/website/components/VTSequence.tsx
@@ -45,6 +45,7 @@ function VTElem({ elem }: { elem: string }) {
 const special: { [key: string]: number } = {
   BEL: 0x07,
   BS: 0x08,
+  LF: 0x0a,
   CR: 0x0d,
   ESC: 0x1b,
 };