Emulation: bold off broken and dim not implemented?

Shutting off (20 + attribute) bold is not working, although others implemented (uline and reverse) do, i.e.,

echo -e '\x1B[33m yellow \x1B[1m bold \x1B[21m normal \x1B[m off'
echo -e '\x1B[33m yellow \x1B[4m uline \x1B[24m normal \x1B[m off'
echo -e '\x1B[33m yellow \x1B[7m reverse \x1B[27m normal \x1B[m off'

Oddly enough, changing 21 (bold off) to 22 (dim off) works: echo -e '\x1B[33m yellow \x1B[1m bold \x1B[22m normal \x1B[m off'

… but bold -> dim enable keeps bold on – I thought bold/dim are implemented as mutually exclusive, unlike underline, blink, and reverse that can be added or taken away with either bold or dim? At the very least if dim is not implemented, it should shutoff bold, but it does not: echo -e '\x1B[33m yellow \x1B[1m bold \x1B[2m dim \x1B[m off'

Two related questions:

1. I get blink (at least for now 😉 not implemented, but how about dim and italic?
2. Can a custom color palette be constructed? The one in v3 branch (below) is more palatable to me.

Details

• Browser and browser version: Firefox 56 (64-bit)
• OS version: Fedora 26 (linux)
• xterm.js version: 2.9.2 and latest v3 branch

Steps to reproduce

$ cat bin/ansi-test.sh
#!/bin/sh

alias print='echo -en'
alias println='echo -e'
csi="\\x1B["
color=( black red green yellow blue magenta cyan white )
attr=( reset bright dim italic uline blink 6 reverse )

for bg in `seq 0 7`; do
        print "(${csi}m${bg}) BG ${csi}0;1;$((30+${bg}))m ${color[${bg}]}${csi}m"
        for fg in `seq 0 7`; do
                print "\n    FG ${csi}0;1;$((30+${fg}))m ${color[${fg}]}${csi}m\t"
                print "${csi}$((40+${bg}))m"
                print "${csi}$((30+${fg}))m"
                for ca in `seq 1 7`; do
                        print "${csi}${ca}m  ${attr[${ca}]}  ${csi}$((20+${ca}))m"
                done
                print "${csi}m"
        done
        println "${csi}m"
done

Showing Terminology - xterm.js - v3 branch:

[mofux]

I’ll try to create a PR to enable dim support.

[Tyriar]

Related: https://github.com/sourcelair/xterm.js/issues/580