On Tuesday, 16 May 2017 at 15:38:53 UTC, Walter Bright wrote:
It includes DOS and Windows consoles.
Only under specific circumstances. On the VGA hardware, underline shares a bit with blue and needs a register tweaked to make it visible (the default 16 color VGA text mode does NOT display the underline), and only worked on CJK multibyte output on Windows 2000 through Windows 10.
Only recently, with the one of the updates to windows 10, was console underlining added to Windows for English text, as part of their Linux terminal compatibility flag (see: ENABLE_VIRTUAL_TERMINAL_PROCESSING).
Then yours is a unique snowflake, as it's standard for VT-100 emulation (xterm).
It isn't really unique, rxvt treats it as bold and xterm can have it compiled out. I do recognize the sequence and even set the bit (see: https://github.com/adamdruppe/terminal-emulator/blob/master/terminalemulator.d#L1724 ) but then ignore it on the drawing side since blinking is a pointless distraction.
In practice, basic color support is pretty broad and reliable, given you remember that there's a human reading it who can't see poor contrast easily and a large percentage of them cannot reliably tell all colors apart. Underline, however, is not broadly supported by the computer console apis.