TERMS.md: document block-drawing

TERMS.md

@@ -11,24 +11,27 @@ this variable, and your terminal doesn't actually support these sequences,
 you're going to have a bad time.
 
 The following have been established on a Debian Unstable workstation.
+`ccc` is the Terminfo can-change-colors capability. `bce` is background
+color erase. "Blocks" refers to whether the terminal provides its own
+implementation of block-drawing characters, or relies on the font.
 
-| Terminal | `ccc` | `bce` | Recommended environment | Notes |
+| Terminal | `ccc` | `bce` | Blocks | Recommended environment | Notes |
 | -------- | ----- | ----- | ----- | ----- |
-| Linux console | ✔ | ✔ |`TERM=linux` `COLORTERM=24bit` | 8 (512 glyph fonts) or 16 (256 glyph fonts) colors max, but RGB values are downsampled to a 256-index palette. See below. |
-| FBterm | | ? |`TERM=fbterm` | 256 colors, no RGB color. |
-| kmscon | | ? | `TERM=xterm-256color` | No RGB color AFAICT, nor any distinct terminfo entry. |
-| XTerm | | ✔ |`TERM=xterm-256color` `COLORTERM=24bit` | See note about DirectColor. Must configure with `--enable-direct-color`. `TERM=xterm-direct` seems to have the undesirable effect of mapping low RGB values to a palette; I don't yet understand this well. The problem is not seen with the specified configuration. Sixel support when built with `--enable-sixel-graphics` and run in vt340 mode. |
-| XFCE4 Terminal | ✔ | ✔ |`TERM=xfce` `COLORTERM=24bit` | No `xfce-direct` variant exists. |
-| Gnome Terminal | 🗴 | ✔ |`TERM=gnome` `COLORTERM=24bit` | `ccc` support *is* available when run with `vte-256color`. |
-| Konsole | 🗴 | ✔ |`TERM=konsole-direct` | |
-| Alacritty | ✔ | ✔ |`TERM=alacritty` `COLORTERM=24bit` | |
-| Kitty | ✔ | 🗴 |`TERM=kitty-direct` | |
-| Sakura | ✔ | ✔ |`TERM=vte-256color` `COLORTERM=24bit` | No terminfo entry? |
-| mlterm | 🗴 | ✔ |`TERM=mlterm-256color` | Do not set `COLORTERM`. `mlterm-direct` gives strange results. |
-| st | ✔ | ✔ |`TERM=st-256color` `COLORTERM=24bit` | |
-| wterm | | | | |
-| GNU Screen | 🗴 | ✔ |`TERM=screen.OLDTERM` | Must be compiled with `--enable-256color`. `TERM` should typically be `screen.` suffixed by the appropriate `TERM` value for the true connected terminal, e.g. `screen.vte-256color`. See below. |
-| tmux | | | | |
+| Linux console | ✔ | ✔ | N/A | `TERM=linux` `COLORTERM=24bit` | 8 (512 glyph fonts) or 16 (256 glyph fonts) colors max, but RGB values are downsampled to a 256-index palette. See below. |
+| FBterm | | ? | ? | `TERM=fbterm` | 256 colors, no RGB color. |
+| kmscon | | ? | ? | `TERM=xterm-256color` | No RGB color AFAICT, nor any distinct terminfo entry. |
+| XTerm | | ✔ |🗴|`TERM=xterm-256color` `COLORTERM=24bit` | See note about DirectColor. Must configure with `--enable-direct-color`. `TERM=xterm-direct` seems to have the undesirable effect of mapping low RGB values to a palette; I don't yet understand this well. The problem is not seen with the specified configuration. Sixel support when built with `--enable-sixel-graphics` and run in vt340 mode. |
+| XFCE4 Terminal | ✔ | ✔ |? |`TERM=xfce` `COLORTERM=24bit` | No `xfce-direct` variant exists. |
+| Gnome Terminal | 🗴 | ✔ |? |`TERM=gnome` `COLORTERM=24bit` | `ccc` support *is* available when run with `vte-256color`. |
+| Konsole | 🗴 | ✔ |? | `TERM=konsole-direct` | |
+| Alacritty | ✔ | ✔ |🗴|`TERM=alacritty` `COLORTERM=24bit` | |
+| Kitty | ✔ | 🗴 |✔ |`TERM=xterm-kitty` | |
+| Sakura | ✔ | ✔ |? |`TERM=vte-256color` `COLORTERM=24bit` | No terminfo entry? |
+| mlterm | 🗴 | ✔ |? |`TERM=mlterm-256color` | Do not set `COLORTERM`. `mlterm-direct` gives strange results. |
+| st | ✔ | ✔ |? |`TERM=st-256color` `COLORTERM=24bit` | |
+| wterm | | | | | |
+| GNU Screen | 🗴 | ✔ | |`TERM=screen.OLDTERM` | Must be compiled with `--enable-256color`. `TERM` should typically be `screen.` suffixed by the appropriate `TERM` value for the true connected terminal, e.g. `screen.vte-256color`. See below. |
+| tmux | | | | | |
 
 Note that `xfce4-terminal`, `gnome-terminal`, etc. are essentially skinning
 atop the common VTE ("Virtual TErminal") library.