From 1a127dbe01f32b0d6ab0f907424f02749eb6727d Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Sat, 7 Oct 2023 22:05:58 -0700
Subject: [PATCH] website: ech

---
 website/app/vt/ech/page.mdx | 157 ++++++++++++++++++++++++++++++++++++
 1 file changed, 157 insertions(+)
 create mode 100644 website/app/vt/ech/page.mdx

diff --git a/website/app/vt/ech/page.mdx b/website/app/vt/ech/page.mdx
new file mode 100644
index 000000000..c4eec2e97
--- /dev/null
+++ b/website/app/vt/ech/page.mdx
@@ -0,0 +1,157 @@
+import VTSequence from "@/components/VTSequence";
+
+# Erase Character (ECH)
+
+<VTSequence sequence={["CSI", "Pn", "X"]} />
+
+Blank `n` cells beginning with (including) and to the right of the cursor.
+
+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.
+
+The rightmost column that can be erased is the rightmost column of the screen.
+The [right margin](#) has no effect on this sequence.
+
+This sequence always unsets the pending wrap state.
+
+For `n` cells up to the rightmost column, blank the cell by replacing it
+with an empty character with the background color colored according to the
+current SGR state. No other SGR attributes are preserved.
+
+If a multi-cell character would be split, erase the full multi-cell
+character. For example, if "橋" is printed and ECH `n = 1` is issued,
+the full character should be erased even though it takes up two cells.
+Both erased cells are colored with the current background color according
+to the current SGR state.
+
+If [Select Character Selection Attribute (DECSCA)](#TODO) is enabled
+or was the most recently enabled protection mode,
+protected attributes are ignored as if they were never set and the cells
+with them are erased. It does not matter if DECSCA is currently disabled,
+protected attributes are still ignored so long as DECSCA was the
+_most recently enabled_ protection mode.
+
+If DECSCA is not currently enabled and was not the most recently enabled protection
+mode, cells with the protected attribute set are respected and not erased but
+still count towards `n`. It does not matter if the protection attribute for a
+cell was originally set from DECSCA.
+
+## Validation
+
+### ECH V-1: Simple Operation
+
+```bash
+printf "ABC"
+printf "\033[1G"
+printf "\033[2X"
+```
+
+```
+|c_C_____|
+```
+
+### ECH V-2: Erasing Beyond Edge of Screen
+
+```bash
+cols=$(tput cols)
+printf "\033[${cols}G"
+printf "\033[2D"
+printf "ABC"
+printf "\033[D"
+printf "\033[10X"
+```
+
+```
+|_____Ac_|
+```
+
+### ECH V-3: Reset Pending Wrap State
+
+```bash
+cols=$(tput cols)
+printf "\033[${cols}G" # move to last column
+printf "A" # set pending wrap state
+printf "\033[X"
+printf "X"
+```
+
+```
+|_______Xc
+```
+
+### ECH V-4: SGR State
+
+```bash
+printf "ABC"
+printf "\033[1G"
+printf "\033[41m"
+printf "\033[2X"
+```
+
+```
+|c_C_____|
+```
+
+The `c_` cells should both have a red background. All other cells
+remain unchanged in style.
+
+### ECH V-5: Multi-cell Character
+
+```bash
+printf "橋BC"
+printf "\033[1G"
+printf "\033[X"
+printf "X"
+```
+
+```
+|XcBC____|
+```
+
+### ECH V-6: Left/Right Scroll Region Ignored
+
+```bash
+printf "\033[1;1H" # move to top-left
+printf "\033[0J" # clear screen
+printf "\033[?69h" # enable left/right margins
+printf "\033[1;3s" # scroll region left/right
+printf "\033[4G"
+printf "ABC"
+printf "\033[1G"
+printf "\033[4X"
+```
+
+```
+|c___BC____|
+```
+
+### ECH V-7: Protected Attributes Ignored with DECSCA
+
+```bash
+printf "\033V"
+printf "ABC"
+printf "\033[1\"q"
+printf "\033[0\"q"
+printf "\033[1G"
+printf "\033[2X"
+```
+
+```
+|c_C_______|
+```
+
+### ECH V-8: Protected Attributes Respected without DECSCA
+
+```bash
+printf "\033[1\"q"
+printf "ABC"
+printf "\033V"
+printf "\033[1G"
+printf "\033[2X"
+```
+
+```
+|ABC_______|
+```
+
+The cursor remains at `A`.